drm/dp: add LTTPR DP 2.0 DPCD addresses

DP 2.0 brings some new DPCD addresses for PHY repeaters.

Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/def17e2329722f22c35807be26b35590ccb93bfd.1631191763.git.jani.nikula@intel.com