drm/i915/dg2: add DG2 UHBR source rates

DG2 supports DP 2.0 UHBR and 128b/132b channel encoding.

Bspec: 53657, 54034
Acked-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/8f82b7eb76f20f1c4ddd2cc7d1bb31e2173c55a6.1629735412.git.jani.nikula@intel.com