drm/i915: Parse EDID probed modes for DRRS support

This patch and finds out the lowest refresh rate supported for the resolution
same as the fixed_mode.
It also checks the VBT fields to see if panel supports seamless DRRS or not.
Based on above data it marks whether eDP panel supports seamless DRRS or not.
This information is needed for supporting seamless DRRS switch for certain
power saving usecases. This patch is tested by enabling the DRM logs and
user should see whether Seamless DRRS is supported or not.

v2: Daniel's review comments
Modified downclock deduction based on intel_find_panel_downclock

v3: Chris's review comments
Moved edp_downclock_avail and edp_downclock to intel_panel

v4: Jani's review comments.
Changed name of the enum edp_panel_type to drrs_support type.
Change is_drrs_supported to drrs_support of type enum drrs_support_type.

v5: Incorporated Jani's review comments
Modify intel_dp_drrs_initialize to return downclock mode. Support for Gen7
and above.

v6: Incorporated Chris's review comments.
Changed initialize to init in intel_drrs_initialize

v7: Incorporated Jani's review comments.
Removed edp_downclock and edp_downclock_avail. Return NULL explicitly.
Make drrs_state and unnamed struct. Move Gen based check inside drrs_init.

v8: Made changes to track PSR enable/disable throughout system use (instead
of just in the init sequence) for disabling/enabling DRRS. Jani's review
comments.

v9: PSR tracking will be done as part of idleness detection patch. Removed
PSR state tracker in i915_drrs. Jani's review comments.

v10: Added log for DRRS not supported in drrs_init

v11: Modification in drrs_init. suggested by Jani

Signed-off-by: Pradeep Bhat <pradeep.bhat@intel.com>
Signed-off-by: Vandana Kannan <vandana.kannan@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>