x86: i915 needs pgprot_writecombine() and is_io_mapping_possible()

Impact: build fix

Theodore Ts reported that the i915 driver needs these symbols:

 ERROR: "pgprot_writecombine" [drivers/gpu/drm/i915/i915.ko] undefined!
 ERROR: "is_io_mapping_possible" [drivers/gpu/drm/i915/i915.ko] undefined!

Reported-by: Theodore Ts'o <tytso@mit.edu> wrote:
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/mm/iomap_32.c

@@ -20,23 +20,16 @@
 #include <asm/pat.h>
 #include <linux/module.h>
 
-#ifdef CONFIG_X86_PAE
-int
-is_io_mapping_possible(resource_size_t base, unsigned long size)
-{
-	return 1;
-}
-#else
-int
-is_io_mapping_possible(resource_size_t base, unsigned long size)
+int is_io_mapping_possible(resource_size_t base, unsigned long size)
 {
+#ifndef CONFIG_X86_PAE
 	/* There is no way to map greater than 1 << 32 address without PAE */
 	if (base + size > 0x100000000ULL)
 		return 0;
-
+#endif
 	return 1;
 }
-#endif
+EXPORT_SYMBOL_GPL(is_io_mapping_possible);
 
 /* Map 'pfn' using fixed map 'type' and protections 'prot'
  */

arch/x86/mm/pat.c

@@ -11,6 +11,7 @@
 #include <linux/bootmem.h>
 #include <linux/debugfs.h>
 #include <linux/kernel.h>
+#include <linux/module.h>
 #include <linux/gfp.h>
 #include <linux/mm.h>
 #include <linux/fs.h>
@@ -868,6 +869,7 @@ pgprot_t pgprot_writecombine(pgprot_t prot)
 	else
 		return pgprot_noncached(prot);
 }
+EXPORT_SYMBOL_GPL(pgprot_writecombine);
 
 #if defined(CONFIG_DEBUG_FS) && defined(CONFIG_X86_PAT)