From: David Mosberger <davidm@napali.hpl.hp.com>

Here is a simplified version of the earlier /dev/mem cleanup.  This version
of the patch no longer pretends to support uncached accesses via
read()/write().  Instead, all it does is:

- consolidate much of the ugly code in uncached_access()

- move pgprot_noncached() macro to pgtable.h for i386, m68k, ppc, ppc64,
  and x86_64

- fix the ia64 implementation to use efi_mem_attributes() to determine
  the cacheability of an address

Eventually, we may want to replace the #ifdef CONFIG_IA64 with #ifdef
CONFIG_EFI, but we can do this "on demand", if and when EFI-based x86
machines become more common.