MIPS: export has_transparent_hugepage() for modules

MIPS should export its local version of "has_transparent_hugepage"
so that loadable modules (dax) can use it.

Fixes this build error:
ERROR: modpost: "has_transparent_hugepage" [drivers/dax/dax.ko] undefined!

Fixes: fd8cfd300019 ("arch: fix has_transparent_hugepage()")
Reported-by: kernel test robot <[e-mail]>
Signed-off-by: Randy Dunlap <[e-mail]>
Cc: Thomas Bogendoerfer <[e-mail]>
Cc: [e-mail]
Cc: Dan Williams <[e-mail]>
Cc: Vishal Verma <[e-mail]>
Cc: Dave Jiang <[e-mail]>
Cc: [e-mail]
Cc: Hugh Dickins <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Signed-off-by: Thomas Bogendoerfer <[e-mail]>

arch/mips/mm/tlb-r4k.c

···
 	}
 	return mask == PM_HUGE_MASK;
 }
+EXPORT_SYMBOL(has_transparent_hugepage);
 
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE  */