drm: dumb scanout create/mmap for intel/radeon (v3)

This is just an idea that might or might not be a good idea,
it basically adds two ioctls to create a dumb and map a dumb buffer
suitable for scanout. The handle can be passed to the KMS ioctls to create
a framebuffer.

It looks to me like it would be useful in the following cases:
a) in development drivers - we can always provide a shadowfb fallback.
b) libkms users - we can clean up libkms a lot and avoid linking
to libdrm_*.
c) plymouth via libkms is a lot easier.

Userspace bits would be just calls + mmaps. We could probably
mark these handles somehow as not being suitable for acceleartion
so as top stop people who are dumber than dumb.

Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_mode.h

@@ -675,4 +675,5 @@ void radeon_fb_output_poll_changed(struct radeon_device *rdev);
 
 void radeon_crtc_handle_flip(struct radeon_device *rdev, int crtc_id);
 
+int radeon_align_pitch(struct radeon_device *rdev, int width, int bpp, bool tiled);
 #endif