drm/i915/mtl: For DP2.0 10G and 20G rates use MPLLA

Use MPLLA for DP2.0 rates 10G and 20G, when ssc is enabled.

v2: Fix typo in commit message (Animesh)

Reviewed-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230428095433.4109054-7-mika.kahola@intel.com