drm/i915: Move intel_drrs_compute_config() into intel_dp.c

drm/i915: Move intel_drrs_compute_config() into intel_dp.c

intel_drrs_compute_config() is 100% DP specific. DRRS on other
types of encoders wouldn't do any of these M2/N2 calculations
etc. So let's move this into intel_dp.c so all the DP state
calculation is more concentrated into one place.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220331112822.11462-10-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>