uboot-imx

efi_loader: specify UEFI spec revision

Both in the boot and the runtime services tables we have to specify the
UEFI spec revision. The same value is already used for the system
table. So let's use a common constant.

In the boot services table we have to provide the header signature.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Alexander Graf <agraf@suse.de>