efi_loader: Check machine type in the image header

Check FileHeader.Machine to make sure the EFI executable image is built
for the same architecture. For example, 32-bit U-Boot on x86 will print
an error message instead of loading an x86_64 image and crashing.

Signed-off-by: Ivan Gorinov <ivan.gorinov@intel.com>
Signed-off-by: Alexander Graf <agraf@suse.de>