ArmPkg: rewrite vector table population macros

ArmPkg: rewrite vector table population macros

Unfortunately, Clang does not support the use of symbol references in .org
directives, and bails with the following error message when it encounters
them:

  <...>:error: expected assembly-time absolute expression
  .org DebugAgentVectorTable + 0x000

So replace the .org arguments with absolute values, and move the whole
vector table into a subsection with the appropriate alignment, and
starting at .org 0x0. This gives the same protection with respect to
entries that exceed 128 bytes, in a way that Clang supports as well.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19303 6f19259b-4bc3-4df7-8a09-765794883524