drm: Update fbdev fb_fix_screeninfo

If you change the color depth via fbset or some other framebuffer aware
userland application struct fb_fix_screeninfo is not updated to this new
information. This patch fixes this issue. Also the function is changed to
just pass in struct drm_framebuffer so in the future we could use more
fields. I'm hoping some day fix->smem* could be set here :-)

Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>