drm/i915: Remove a few redundant glk checks

Now that glk display version is 10 we can drop a few more glk checks.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210412054607.18133-6-ville.syrjala@linux.intel.com