x86: fix EFI mapping

The patch updates EFI runtime memory mapping code, by making EFI
areas explicitly executable.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>