StandaloneMmPkg: add HobLib implementation for MM_STANDALONE modules

StandaloneMmPkg: add HobLib implementation for MM_STANDALONE modules

This HobLib code is based on the staging implementation of
StandaloneMmPkg, with the following changes:
- drop the unused AArch64/StandaloneMmCoreHobLibInternal.c source file
- remove hack from HobLibConstructor()
- update code comments referring the MM core

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jagadeesh Ujja <jagadeesh.ujja@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Achin Gupta <achin.gupta@arm.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>