MdeModulePkg/PeiCore: allocate BootServicesCode memory for PE/COFF images

MdeModulePkg/PeiCore: allocate BootServicesCode memory for PE/COFF images

Ensure that any memory allocated for PE/COFF images is identifiable as
a boot services code region, so that we know it requires its executable
permissions to be preserved when we tighten mapping permissions later on.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>