drm: Add drm_rect_debug_print()

Add a debug function to print the rectangle in a human readable format.

v2: Renamed drm_region to drm_rect, the function from drm_region_debug
    to drm_rect_debug_print(), and use %+d instead of +%d in the format.
v3: Use %d format for width/height in the non fixed point case as well

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>