drm/i915/dp: fix EHL/JSL max source rates calculation

Only higher voltage sku can support HBR3 so a condition
check added in max source rate calculation for ehl/jsl.

Bspec: 32247, 20598

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Animesh Manna <animesh.manna@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210901160402.24816-4-animesh.manna@intel.com