drm/sun4i: Use (struct drm_format_info) fields to determine if a format is yuv and multi planar or not.

We do not need sun4i_backend_format_is_packed_yuv422() /
sun4i_backend_format_is_planar_yuv() to determine if the format is yuv multi planar
or not. (struct drm_format_info *)->is_yuv tells if the format is yuv or not.
And (struct drm_format_info *)->num_planes denotes the number of planes.

This issue was identified during a review on a previous patch:-
https://lists.freedesktop.org/archives/dri-devel/2018-July/183840.htmlSigned-off-by: Ayan Kumar halder <ayan.halder@arm.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1532336220-3791-1-git-send-email-ayan.halder@arm.com