drm/i915/gvt: drop checks for early Skylake revisions

drm/i915/gvt: drop checks for early Skylake revisions

We no longer cater for pre-production revisions of Skylake.

Fixes: d4362225e8cb ("drm/i915/gvt: update misc ctl regs base on stepping info")
Cc: Ping Gao <[email protected]>
Cc: Zhenyu Wang <[email protected]>
Cc: Zhi Wang <[email protected]>
Cc: <[email protected]>
Signed-off-by: Jani Nikula <[email protected]>
Reviewed-by: Paulo Zanoni <[email protected]>
Signed-off-by: Zhenyu Wang <[email protected]>