drm/i915: Set scaler mode for NV12

This patch sets appropriate scaler mode for NV12 format.
In this mode, skylake scaler does either chroma-upsampling or
chroma-upsampling and resolution scaling

v2: Review comments from Ville addressed
NV12 case to be checked first for setting
the scaler

v3: Rebased (me)

v4: Rebased (me)

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)
Restricting the NV12 change for scaler to BXT and KBL
in this series.

v9: Rebased (me)

v10: As of now, NV12 has been tested on Gen9 and Gen10. However,
code is applicable to all GEN >= 9. Hence making
that change to keep it generic.
Comments under v8 is not valid anymore.

v11: Addressed review comments by Shashank Sharma.
For Gen10+, the scaler mode to be set it planar or normal
(single bit). Changed the code to be applicable to all
Gen.

v12: Addressed review comments from Shashank Sharma
For Gen9 (apart from GLK) bits 28:29 to be programmed
in PS_CTRL for NV12. For GLK and Gen10+, bit 29 to be set
for all Planar.

v13: Addressed review comments from Juha-Pekka Heikkila
"NV12 not to be supported by SKL"
Adding Reviewed by tag from Shashank Shamr

v14: Added reviewed by from Juha-Pekka Heikkila

v15: Rebased the series

Tested-by: Clinton Taylor <clinton.a.taylor@intel.com>
Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>
Reviewed-by: Clinton Taylor <clinton.a.taylor@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/1523245273-30264-13-git-send-email-vidya.srinivas@intel.com