ArmPkg/DefaultExceptionHandlerLib ARM: avoid endless loop in RELEASE builds

ArmPkg/DefaultExceptionHandlerLib ARM: avoid endless loop in RELEASE builds

Ensure that we prevent the CPU from proceeding after having taken an
unhandled exception on a RELEASE build, which does not contain the
ASSERT() which ensures this on DEBUG and NOOPT builds.

Retain the code following the deadloop so that we can keep going when
running in a debugger.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>