efi_loader: Add PE image loader

EFI uses the PE binary format for its application images. Add support to EFI PE
binaries as well as all necessary bits for the "EFI image loader" interfaces.

Signed-off-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>