MdePkg/DxeServicesLib: introduce AllocatePeiAccessiblePages routine

MdePkg/DxeServicesLib: introduce AllocatePeiAccessiblePages routine

Add a routine to DxeServicesLib that abstracts the allocation of memory
that should be accessible by PEI after resuming from S3. We will use it
to replace open coded implementations that limit the address to < 4 GB,
which may not be possible on non-Intel systems that have no 32-bit
addressable memory at all.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>