MdeModulePkg/EbcDxe: implement the PE/COFF emulator protocol

Implement the new EDK2 PE/COFF image emulator protocol so that we can
remove the EBC specific handling in the DXE core and other places in
the core code.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Hao Wu <hao.a.wu@intel.com>