drm: Print the fb dimensions when the src coord check fails

When debugging bad plane source coordinates it helps to have an
idea of what the framebuffer dimensions are.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171101183533.28466-1-ville.syrjala@linux.intel.com