ArmPkg: Dispatch deferred images after EndOfDxe

ArmPkg: Dispatch deferred images after EndOfDxe

Third party driver images loaded from Option ROM get queued
for execution after EndOfDxe. These queued images need to be
dispatched from the PlatformBootManagerLib.

Since the queued images were not dispatched, the PCI Option
ROM drivers were not getting loaded on Juno. Therefore,
add call to EfiBootManagerDispatchDeferredImages() for
dispatching deferred images from PlatformBootManagerLib.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>