drm/i915/dp: Compute DSC pipe config in atomic check

DSC params like the enable, compressed bpp, slice count and
dsc_split are added to the intel_crtc_state. These parameters
are set based on the requested mode and available link parameters
during the pipe configuration in atomic check phase.
These values are then later used to populate the remaining DSC
and RC parameters before enbaling DSC in atomic commit.

v15:
* Rebase over drm-tip
v14:
Remove leftovers, use dsc_bpc, refine dsc_compute_config (Ville)
v13:
* Compute DSC bpc only when DSC is req to be enabled (Ville)
v12:
* Override bpp with dsc dpcd color depth (Manasi)
v11:
* Const crtc_state, reject DSC on DP without FEC (Ville)
* Dont set dsc_split to false (Ville)
v10:
* Add a helper for dp_dsc support (Ville)
* Set pipe_config to max bpp, link params for DSC for now (Ville)
* Compute bpp - use dp dsc support helper (Ville)
v9:
* Rebase on top of drm-tip that now uses fast_narrow config
for edp (Manasi)
v8:
* Check for DSC bpc not 0 (manasi)

v7:
* Fix indentation in compute_m_n (Manasi)

v6 (From Gaurav):
* Remove function call of intel_dp_compute_dsc_params() and
invoke intel_dp_compute_dsc_params() in the patch where
it is defined to fix compilation warning (Gaurav)

v5:
Add drm_dsc_cfg in intel_crtc_state (Manasi)

v4:
* Rebase on refactoring of intel_dp_compute_config on tip (Manasi)
* Add a comment why we need to check PSR while enabling DSC (Gaurav)

v3:
* Check PPR > max_cdclock to use 2 VDSC instances (Ville)

v2:
* Add if-else for eDP/DP (Gaurav)

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Cc: Gaurav K Singh <gaurav.k.singh@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Reviewed-by: Ville Syrjala <ville.syrjala@linux.intel.com>
Acked-by: Jani Nikula <jani.nikula@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181128213621.21391-1-manasi.d.navare@intel.com