drm/i915: Cleanup modesetting on load-error path

After handling a critical failure initialising GEM we need to unwind the
modesetting setup.

Testcase: igt/drv_module_reload/basic-reload-inject
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180710094421.16223-2-chris@chris-wilson.co.uk


Reviewed-by: Matthew Auld <matthew.auld@intel.com>