drm/i915/mtl: Add voltage swing sequence for C20

DP1.4 and DP20 voltage swing sequence for C20 phy.

Bspec: 65449, 67636, 67610

Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Clint Taylor <Clinton.A.Taylor@intel.com>
Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230428095433.4109054-6-mika.kahola@intel.com