drm/i915/dg2: add SNPS PHY translations for UHBR link rates

UHBR link rates use different tx equalization settings. Using this will
require changes in the link training code too.

Bspec: 53920
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210813115151.19290-3-jani.nikula@intel.com