So far, the drm_format_plane_height/width functions were operating on the
format's fourcc and was doing a lookup to retrieve the drm_format_info
structure and return the cpp.

However, this is inefficient since in most cases, we will have the
drm_format_info pointer already available so we shouldn't have to perform a
new lookup. Some drm_fourcc functions also already operate on the
drm_format_info pointer for that reason, so the API is quite inconsistent
there.

Let's follow the latter pattern and remove the extra lookup while being a
bit more consistent.

In order to be extra consistent, also rename that function to
drm_format_info_plane_cpp and to a static function in the header to match
the current policy. The parameters order have also be changed to match the
other functions prototype.
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/514af1d489d80b8b1767e3716b663ce5103da6eb.1558002671.git-series.maxime.ripard@bootlin.com