drm/i915: Define explicit wedged on init reset state

We're currently using scratch presence as a way of identifying that we
entered wedged state at driver initialization time.
Let's use a separate flag rather than rely on scratch.

Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190926133142.2838-1-chris@chris-wilson.co.uk