Restore some defines in xlat_tables.h ...

Commit e8719552a24 removed some definitions related to translation
tables from the xlat_tables.h header file, based on the assumption
that they weren't used by any platform. These are actually used by
some partners so this patch restores them.

Fixes ARM-software/tf-issues#425

Change-Id: Idafa5f00bb0bd9c2847b5ae6541cf8db93c7b89a

Automatically select initial xlation lookup level ...

Instead of hardcoding a level 1 table as the base translation level
table, let the code decide which level is the most appropriate given
the virtual address space size.

As the table granularity is 4 KB, this allows the code to select
level 0, 1 or 2 as base level for AArch64. This way, instead of
limiting the virtual address space width to 39-31 bits, widths of
48-25 bit can be used.

For AArch32, this change allows the code to select level 1 or 2
as the base translation level table and use virtual address space
width of 32-25 bits.

Also removed some unused definitions related to translation tables.

Fixes ARM-software/tf-issues#362

Change-Id: Ie3bb5d6d1a4730a26700b09827c79f37ca3cdb65

AArch32: Add translation table library support ...

This patch adds translation library supports for AArch32 platforms.
The library only supports long descriptor formats for AArch32.
The `enable_mmu_secure()` enables the MMU for secure world with
`TTBR0` pointing to the populated translation tables.

Change-Id: I061345b1779391d098e35e7fe0c76e3ebf850e08

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: Remove out-dated comment ...

As of commit e1ea9290bb, if the attributes of an inner memory region
are different than the outer region, new page tables are generated
regardless of how "restrictive" they are. This patch removes an
out-dated comment still referring to the old priority system based
on which attributes were more restrictive.

Change-Id: Ie7fc1629c90ea91fe50315145f6de2f3995e5e00

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