If the source and sink support MSO, enable it during link training.

v4: Divide DRRS pixel clock by link count before M/N calculation

v3: Adjust timings, refer to splitter

v2: Limit MSO to pipe A using ->pipe_mask

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2711
Cc: Nischal Varide <nischal.varide@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/66da48b4b3c5ccffaac7989097cd96d6c6af8243.1614682842.git.jani.nikula@intel.com