drm: Add drm_framebuffer_plane_{width,height}()

Add variants of drm_format_plane_{width,height}() that take an entire fb
object instead of just the format. These should be more efficent as they
can just look up the format info from the fb->format pointer rather than
having to look it up (using a linear search based on the format).

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1479498793-31021-30-git-send-email-ville.syrjala@linux.intel.com