drm/i915: Add skl_check_nv12_surface for NV12

We skip src trunction/adjustments for
NV12 case and handle the sizes directly.
Without this, pipe fifo underruns are seen on APL/KBL.

v2: For NV12, making the src coordinates multiplier of 4

v3: Moving all the src coords handling code for NV12
to skl_check_nv12_surface

v4: Added RB from Mika

v5: Rebased the series. Removed checks of mult of 4 in
skl_update_scaler, Added NV12 condition in intel_check_sprite_plane
where src x/w is being checked for mult of 2 for yuv planes.

v6: Made changes to skl_check_nv12_surface as per WA#1106

Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Vidya Srinivas <vidya.srinivas@intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1526074397-10457-4-git-send-email-vidya.srinivas@intel.com