Add header guards to asm macro files ...

Some assembly files containing macros are included like header files
into other assembly files. This will cause assembler errors if they
are included multiple times.

Add header guards to assembly macro files to avoid assembler errors.

Change-Id: Ia632e767ed7df7bf507b294982b8d730a6f8fe69

Rework use of labels in assembly macros. ...

This patch provides a workaround for the ASM_ASSERT label issue
and also reworks the use of labels in assembly macros.
If the caller of the ASM_ASSERT macro happened to use the
label '1' to jump past the ASM_ASSERT macro, it would not have
worked since the ASM_ASSERT macro internally used the same label.
Hence, as a workaround, this patch makes the label a high
number in the expectation that the caller will never use it.

Also updated the other assembly macros using numerical labels to
named lables.

Change-Id: Iec892359db84f2391ad2a83a92141c4d7049776a

Implement an assert() callable from assembly code ...

The patch implements a macro ASM_ASSERT() which can
be invoked from assembly code. When assertion happens,
file name and line number of the check is written
to the crash console.

Fixes ARM-software/tf-issues#95

Change-Id: I6f905a068e1c0fa4f746d723f18df60daaa00a86