drm/fb: add more correct 8/16/24/32 bpp fb support.

The previous patches had some unwanted side effects, I've fixed
the lack of 32bpp working, and fixed up 16bpp so it should also work.

this also adds the interface to allow the driver to set a preferred
console depth so for example low memory rn50 can set it to 8bpp.
It also catches 24bpp on cards that can't do it and forces 32bpp.

Tested on r100/r600/i945.

Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index b9e47f1..aa96b52 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -173,6 +173,8 @@
 extern void intelfb_restore(void);
 extern void intel_crtc_fb_gamma_set(struct drm_crtc *crtc, u16 red, u16 green,
 				    u16 blue, int regno);
+extern void intel_crtc_fb_gamma_get(struct drm_crtc *crtc, u16 *red, u16 *green,
+				    u16 *blue, int regno);
 
 extern int intel_framebuffer_create(struct drm_device *dev,
 				    struct drm_mode_fb_cmd *mode_cmd,