drm/i915/display: Remove check for low voltage sku for max dp source rate

The low voltage sku check can be ignored as OEMs need to consider that
when designing the board and then put any limits in VBT.

Same is now changed in Bspec pages.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5272

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@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/20220315080247.1161844-2-ankit.k.nautiyal@intel.com