drm/i915: Clean up some expressions

Write the '!(SNB||IVB)' checks in the CPT/PPT detections
as '!SNB && !IVB' to make it less messy looking, and clear out
some useless parens the from the virtualization PCH detection case.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170620130310.13245-5-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>