mm: move phys_mem_access_prot_allowed() declaration to pgtable.h

We get 1 warning when building kernel with W=1:

drivers/char/mem.c:220:12: warning: no previous prototype for 'phys_mem_access_prot_allowed' [-Wmissing-prototypes]
int __weak phys_mem_access_prot_allowed(struct file *file,

In fact, its declaration is spreading to several header files in
different architecture, but need to be declare in common header file.

So this patch moves phys_mem_access_prot_allowed() to pgtable.h.

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Baoyou Xie <[e-mail]>
Acked-by: Thomas Gleixner <[e-mail]>
Acked-by: Ralf Baechle <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/mips/include/asm/pgtable.h

···
 struct file;
 pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
 		unsigned long size, pgprot_t vma_prot);
-int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,
-		unsigned long size, pgprot_t *vma_prot);
 #endif
 
 /*

arch/x86/include/asm/pgtable_types.h

···
 struct file;
 pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
                               unsigned long size, pgprot_t vma_prot);
-int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,
-                              unsigned long size, pgprot_t *vma_prot);
 
 /* Install a pte for a particular vaddr in kernel space. */
 void set_pte_vaddr(unsigned long vaddr, pte_t pte);

include/asm-generic/pgtable.h

···
 #endif
 #endif
 
+struct file;
+int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,
+			unsigned long size, pgprot_t *vma_prot);
 #endif /* !__ASSEMBLY__ */
 
 #ifndef io_remap_pfn_range