EmulatorPkg/PlatformBds: Signal EndOfDxe in platform BDS

EmulatorPkg/PlatformBds: Signal EndOfDxe in platform BDS

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1079

Without signal of EndOfDxe, the 3rd party code (.efi from non-flash
storage) cannot run. It's forbidden by
8be37a5cee700777ca8e8e8a34cc2225b21931a7
*MdeModulePkg/SecurityStubDxe: Defer 3rd party image before EndOfDxe

The patch enables running of SCT from internal shell.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Hao A Wu <hao.a.wu@intel.com>
Cc: Andrew Fish <afish@apple.com>