drm/i915: Capture max frl rate for PCON in dfp cap structure

HDMI2.1 PCON advertises Max FRL bandwidth supported by the PCON.

This patch captures this in dfp cap structure in intel_dp and uses
this to prune connector modes that cannot be supported by the PCON
and FRL bandwidth.

v2: Addressed review comments from Uma Shankar:
-tweaked the comparison of target bw and pcon frl bw to avoid roundup errors.
-minor modification of field names and comments.

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201218103723.30844-9-ankit.k.nautiyal@intel.com