NOMMU: Stub out vm_get_page_prot() if there's no MMU

Stub out vm_get_page_prot() if there's no MMU.

This was added by commit 804af2cf ("[AGPGART] remove private page
protection map") and is used in commit c07fbfd1 ("fbmem: VM_IO set,
but not propagated") in the fbmem video driver, but the function doesn't
exist on NOMMU, resulting in an undefined symbol at link time.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Reviewed-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

include/linux/mm.h

@@ -1363,7 +1363,15 @@ static inline unsigned long vma_pages(struct vm_area_struct *vma)
 	return (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
 }
 
+#ifdef CONFIG_MMU
 pgprot_t vm_get_page_prot(unsigned long vm_flags);
+#else
+static inline pgprot_t vm_get_page_prot(unsigned long vm_flags)
+{
+	return __pgprot(0);
+}
+#endif
+
 struct vm_area_struct *find_extend_vma(struct mm_struct *, unsigned long addr);
 int remap_pfn_range(struct vm_area_struct *, unsigned long addr,
 			unsigned long pfn, unsigned long size, pgprot_t);