xlat lib: Introduce MT_EXECUTE/MT_EXECUTE_NEVER attributes ...

This patch introduces the MT_EXECUTE/MT_EXECUTE_NEVER memory mapping
attributes in the translation table library to specify the
access permissions for instruction execution of a memory region.
These new attributes should be used only for normal, read-only
memory regions. For other types of memory, the translation table
library still enforces the following rules, regardless of the
MT_EXECUTE/MT_EXECUTE_NEVER attribute:

 - Device memory is always marked as execute-never.
 - Read-write normal memory is always marked as execute-never.

Change-Id: I8bd27800a8c1d8ac1559910caf4a4840cf25b8b0

xlat lib: Refactor mmap_desc() function ...

This patch clarifies the mmap_desc() function by adding some comments
and reorganising its code. No functional change has been introduced.

Change-Id: I873493be17b4e60a89c1dc087dd908b425065401

Fix computation of L1 bitmask in the translation table lib ...

This patch fixes the computation of the bitmask used to isolate
the level 1 field of a virtual address. The whole computation needs
to work on 64-bit values to produce the correct bitmask value.
XLAT_TABLE_ENTRIES_MASK being a C constant, it is a 32-bit value
so it needs to be extended to a 64-bit value before it takes part
in any other computation.

This patch fixes this bug by casting XLAT_TABLE_ENTRIES_MASK as
an unsigned long long.

Note that this bug doesn't manifest itself in practice because
address spaces larger than 39 bits are not yet supported in the
Trusted Firmware.

Change-Id: I955fd263ecb691ca94b29b9c9f576008ce1d87ee

Limit support for region overlaps in xlat_tables ...

The only case in which regions can now overlap is if they are
identity mapped or they have the same virtual to physical address
offset (identity mapping is just a particular case of the latter).
They must overlap completely (i.e. one of them must be completely
inside the other one) and not cover the same area.

This allow future enhancements to the xlat_tables library without
having to support unnecessarily complex edge cases.

Outer regions are now sorted by mmap_add_region() before inner
regions with the same base virtual address for consistency: all
regions contained inside another one must be placed after the outer
one in the list.

If an inner region has the same attributes as the outer ones it will
be merged when creating the tables with init_xlation_table(). This
cannot be done as regions are added because there may be cases where
adding a region makes previously mergeable regions no longer
mergeable.

If the attributes of an inner region are different than the outer
region, new pages will be generated regardless of how "restrictive"
they are. For example, RO memory is more restrictive than RW. The
old implementation would give priority to RO if there is an overlap,
the new one doesn't.

NOTE: THIS IS THEORETICALLY A COMPATABILITY BREAK FOR PLATFORMS THAT
USE THE XLAT_TABLES LIBRARY IN AN UNEXPECTED WAY. PLEASE RAISE A
TF-ISSUE IF YOUR PLATFORM IS AFFECTED.

Change-Id: I75fba5cf6db627c2ead70da3feb3cc648c4fe2af

Refactor the xlat_tables library code ...

The AArch32 long descriptor format and the AArch64 descriptor format
correspond to each other which allows possible sharing of xlat_tables
library code between AArch64 and AArch32. This patch refactors the
xlat_tables library code to seperate the common functionality from
architecture specific code. Prior to this patch, all of the xlat_tables
library code were in `lib/aarch64/xlat_tables.c` file. The refactored code
is now in `lib/xlat_tables/` directory. The AArch64 specific programming
for xlat_tables is in `lib/xlat_tables/aarch64/xlat_tables.c` and the rest
of the code common to AArch64 and AArch32 is in
`lib/xlat_tables/xlat_tables_common.c`. Also the data types used in
xlat_tables library APIs are reworked to make it compatible between AArch64
and AArch32.

The `lib/aarch64/xlat_tables.c` file now includes the new xlat_tables
library files to retain compatibility for existing platform ports.
The macros related to xlat_tables library are also moved from
`include/lib/aarch64/arch.h` to the header `include/lib/xlat_tables.h`.

NOTE: THE `lib/aarch64/xlat_tables.c` FILE IS DEPRECATED AND PLATFORM PORTS
ARE EXPECTED TO INCLUDE THE NEW XLAT_TABLES LIBRARY FILES IN THEIR MAKEFILES.

Change-Id: I3d17217d24aaf3a05a4685d642a31d4d56255a0f