Empirical evidence from CI tells us that our rc6 setup for Tigerlake is
off. Disable rc6 on tgl temporary so that we gain CI coverage as we
prepare a fix. It also appears that the BIOS on our tgl leaves rc6
enabled, so we have to explicitly disable it on init.

References: https://bugs.freedesktop.org/show_bug.cgi?id=111593Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Acked-by: NMatthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190910161657.23037-1-chris@chris-wilson.co.uk