Export tiny shmem_file_setup for DRM-GEM

We're trying to keep the !CONFIG_SHMEM tiny-shmem.c (using ramfs without
swap) in synch with CONFIG_SHMEM shmem.c (and mpm is preparing patches
to combine them). I was glad to see EXPORT_SYMBOL_GPL(shmem_file_setup)
go into shmem.c, but why not support DRM-GEM when !CONFIG_SHMEM too?
But caution says still depend on MMU, since !CONFIG_MMU is.. different.

Signed-off-by: Hugh Dickins <[e-mail]>
Acked-by: Matt Mackall <[e-mail]>
Acked-by: Dave Airlie <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/gpu/drm/Kconfig

···
 #
 menuconfig DRM
 	tristate "Direct Rendering Manager (XFree86 4.1.0 and higher DRI support)"
-	depends on (AGP || AGP=n) && PCI && !EMULATED_CMPXCHG && SHMEM
+	depends on (AGP || AGP=n) && PCI && !EMULATED_CMPXCHG && MMU
 	help
 	  Kernel-level support for the Direct Rendering Infrastructure (DRI)
 	  introduced in XFree86 4.0. If you say Y here, you need to select

mm/tiny-shmem.c

···
 put_memory:
 	return ERR_PTR(error);
 }
+EXPORT_SYMBOL_GPL(shmem_file_setup);
 
 /**
  * shmem_zero_setup - setup a shared anonymous mapping