drm/i915/dp: Do not enable PSR2 if DSC is enabled

drm/i915/dp: Do not enable PSR2 if DSC is enabled

If a eDP panel supports both PSR2 and VDSC, our HW cannot
support both at a time. Give priority to PSR2 if a requested
resolution can be supported without compression else enable
VDSC and keep PSR2 disabled.

v4:
Fix the unrealted stuff removed during rebase (Ville)
v3:
* Rebase
v2:
* Add warning for DSC and PSR2 enabled together (DK)

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181128202628.20238-3-manasi.d.navare@intel.com