gallium: check all planes' pipe formats in case of multi-samplers

Current code only checks whether first plane's format is supported
in case YUV format sampling is done by sampling each plane separately.
It would be safer to check other planes' as well.

Signed-off-by: Dongwon Kim <dongwon.kim@intel.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/2863>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/2863>