x86: efi: Add EFI loader support for x86

x86: efi: Add EFI loader support for x86

Add the required pieces to support the EFI loader on x86.

Since U-Boot only builds for 32-bit on x86, only a 32-bit EFI application
is supported. If a 64-bit kernel must be booted, U-Boot supports this
directly using FIT (see doc/uImage.FIT/kernel.its). U-Boot can act as a
payload for both 32-bit and 64-bit EFI.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Alexander Graf <agraf@suse.de>