x86 PAT: consolidate old memtype new memtype check into a function

Impact: cleanup

Move the new memtype old memtype allowed check to header so that is can be
shared by other users. Subsequent patch uses this in pat.c in remap_pfn_range()
code path. No functionality change in this patch.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/pci/i386.c b/arch/x86/pci/i386.c
index f884740..5ead808 100644
--- a/arch/x86/pci/i386.c
+++ b/arch/x86/pci/i386.c
@@ -314,17 +314,7 @@
 		return retval;
 
 	if (flags != new_flags) {
-		/*
-		 * Do not fallback to certain memory types with certain
-		 * requested type:
-		 * - request is uncached, return cannot be write-back
-		 * - request is uncached, return cannot be write-combine
-		 * - request is write-combine, return cannot be write-back
-		 */
-		if ((flags == _PAGE_CACHE_UC_MINUS &&
-		     (new_flags == _PAGE_CACHE_WB)) ||
-		    (flags == _PAGE_CACHE_WC &&
-		     new_flags == _PAGE_CACHE_WB)) {
+		if (!is_new_memtype_allowed(flags, new_flags)) {
 			free_memtype(addr, addr+len);
 			return -EINVAL;
 		}