ArmPkg: Replace single dead loop.

ArmPkg: Replace single dead loop.

Several assembler macros use a loop at the label "dead" to trap an error.
This is difficult to debug as there is no indication of how one arrived at the loop.
This change replaces dead with distinct loops locally in the macro,
which means the cause of the hang is detectable to the debugger.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15273 6f19259b-4bc3-4df7-8a09-765794883524