drm/i915: Check caller held wakerefs in assert_forcewakes_active

The intent of the assert is to document that the caller took the
appropriate wakerefs for the function. However, as Tvrtko pointed out,
we simply check whether the fw_domains are active and may be confused by
the auto wakeref which may be dropped between the check and use. Let's
be more careful in the assert and check that each fw_domain has an
explicit caller wakeref above and beyond the automatic wakeref.

v2: Fix spelling for config DRM_I915_DEBUG_RUNTIME_PM
v3: Timer may still be active after we drop the autowakeref, we need to
check domain->active instead.
v4: The timer checks domain->active, but we still need to check the
timer. (This is starting to look weird...)

Reported-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190704102048.6436-1-chris@chris-wilson.co.uk