drm/i915: Query the vswing levels per-lane for icl mg phy

Prepare for per-lane drive settings by querying the desired vswing
level per-lane.

Note that the code only does two loops, with each one writing the
levels for two TX lanes.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211006204937.30774-10-ville.syrjala@linux.intel.com


Reviewed-by: José Roberto de Souza <jose.souza@intel.com>