efi_loader: efi_guid_t must be 64-bit aligned

The UEFI Specification Version 2.7 Errata A defines:

"EFI_GUID
128-bit buffer containing a unique identifier value.
Unless otherwise specified, aligned on a 64-bit boundary."

Before this patch efi_guid_t was 8-bit aligned.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Alexander Graf <agraf@suse.de>