[ Upstream commit 7ed43df720c007d60bee6d81da07bcdc7e4a55ae ]

If we fail during GEM initialisation, we scrub the HW state by
performing a device level GPU resuet. However, we want to leave the
system in a usable state (with functioning KMS but no GEM) so after
scrubbing the HW state, we need to restore some sane defaults and
re-enable the low-level common parts of the GPU (such as the GMCH).

v2: Restore GTT entries.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180726085033.4044-2-chris@chris-wilson.co.ukReviewed-by: NMichał Winiarski <michal.winiarski@intel.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>