drm/i915/ehl: Support HBR3 on EHL combo PHY

Unlike ICL, EHL's combo PHYs can support HBR3 data rates.  Note that
this just extends the upper limit; we will continue to honor the max
data rate specified in the VBT in cases where it is lower than HBR3.

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190605211832.23945-1-matthew.d.roper@intel.com


Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>