XEN: EFI: Move x86 specific codes to architecture directory

XEN: EFI: Move x86 specific codes to architecture directory

Move x86 specific codes to architecture directory and export those EFI
runtime service functions. This will be useful for initializing runtime
service on ARM later.

Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Tested-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
(cherry picked from commit a62ed500307bfaf4c1a818b69f7c1e7df1039a16)
Signed-off-by: Bob Liu <bob.liu@oracle.com>
Orabug: 24820937

 Conflicts:
	drivers/xen/efi.c