drm/i915: Use GEM suspend when aborting initialisation

As part of our GEM initialisation now, we send a request to the hardware
in order to record the initial GPU state. This coupled with deferred
idle workers, makes aborting on error tricky. We already have the
mechanism in place to wait on the GPU and cancel all the deferred
workers for suspend, so let's reuse it during the error teardown. It is
already used in places for later init error handling, but doing so at
this point is slightly ugly due to the mutex dance (it's ok, the module
load is still single threaded).

Testcase: igt/drv_module_reload/basic-reload-inject
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Michał Winiarski <michal.winiarski@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180606145441.4460-1-chris@chris-wilson.co.uk