drm/i915: Stop calling intel_opregion unregister/register in suspend/resume

If we reduce the suspend function for intel_opregion to do the minimum
required, the resume function can also do the simple task of notifier
the ACPI bios that we are back. This avoid some nasty restrictions on
the likes of register_acpi_notifier() that are not allowed during the
early phase of resume.

v2: Keep the order of acpi notify vs turning off ardy/drdy the same.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181030110554.4111-1-chris@chris-wilson.co.uk