x86: efi: Refactor the directory of EFI app and payload support

x86: efi: Refactor the directory of EFI app and payload support

At present the EFI application and payload support codes in the x86
directory is distributed in a hybrid way. For example, the Kconfig
options for both app and payload are in arch/x86/lib/efi/Kconfig,
but the source codes in the same directory get built only for
CONFIG_EFI_STUB.

This refactors the codes by consolidating all the EFI support codes
into arch/x86/cpu/efi, just like other x86 targets.

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