drm/i915/display/dp: Attach and set drm connector VRR property

This function sets the VRR property for connector based
on the platform support, EDID monitor range and DP sink
DPCD capability of outputing video without msa
timing information.

v8:
* Use HAS_VRR, remove drm_conn declaration (Jani N)
* Fix typos in Comment (Jani N)
v7:
* Move the helper to separate file (Manasi)
v6:
* Remove unset of prop
v5:
* Fix the vrr prop not being set in kernel (Manasi)
* Unset the prop on connector disconnect (Manasi)
v4:
* Rebase (Mansi)
v3:
* intel_dp_is_vrr_capable can be used for debugfs, make it
non static (Manasi)
v2:
* Just set this in intel_dp_get_modes instead of new hook (Jani)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Aditya Swarup <aditya.swarup@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210122232647.22688-2-manasi.d.navare@intel.com