x86: fix some bugs about EFI runtime code mapping

This patch fixes some bugs of making EFI runtime code executable.

- Use change_page_attr in i386 too. Because the runtime code may be
  mapped not through ioremap.

- If there is no _PAGE_NX in __supported_pte_mask, the change_page_attr
  is not called.

- Make efi_ioremap map pages as PAGE_KERNEL_EXEC_NOCACHE, because EFI runtime
  code may be mapped through efi_ioremap.

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>