drm/i915: Use correct fw_domains during initialisation

In the next patch we will begin to sanity check that we do not attempt
to obtain the forcewake on an unsupport domain. However, that is exactly
what we do during our actual initialisation of fw_domains - rectify it
before it explodes.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170323101944.21627-2-chris@chris-wilson.co.uk