drm/i915: Update format_is_yuv() to include NV12

This patch adds NV12 to format_is_yuv() function
for sprite planes.

v2:
-Use intel_ prefix for format_is_yuv (Ville)

v3: Rebased (me)

v4: Rebased and addressed review comments from Clinton A Taylor.
"static function in intel_sprite.c is not available
to the primary plane functions".
Changed commit message - function modified for
sprite planes.

v5: Missed the Tested-by/Reviewed-by in the previous series
Adding the same to commit message in this version.

v6: Rebased (me)

v7: Rebased (me)

v8: Rebased (me)

v9: Rebased (me)

v10: Changed intel_format_is_yuv function from
static to non-static. We need to use it later from
other files for check.

v11: Rebased the patch. format_is_yuv has already
been renamed to intel_format_is_yuv in the color
patch series which is already merged. This function
which was previously static has already been made
non-static. So this patch after rebase just adds
NV12 to intel_format_is_yuv function.

v12: Added reviewed by from Juha-Pekka Heikkila

v13/v14/v15: Rebased the series

Tested-by: Clinton Taylor <clinton.a.taylor@intel.com>
Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Reviewed-by: Clinton Taylor <clinton.a.taylor@intel.com>
Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>
Signed-off-by: Chandra Konduru <chandra.konduru@intel.com>
Signed-off-by: Nabendu Maiti <nabendu.bikash.maiti@intel.com>
Signed-off-by: Vidya Srinivas <vidya.srinivas@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1523245273-30264-14-git-send-email-vidya.srinivas@intel.com