drm/i915: Only mark the ctx as initialised after a SET_CONTEXT operation

Fallout from

commit 46470fc9
Author: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Date:   Wed May 21 19:01:06 2014 +0300

    drm/i915: Add null state batch to active list

undid the earlier fix of only marking the ctx as initialised after it is
saved by the hardware during a SET_CONTEXT operation:

commit ad1d2199
Author: Ben Widawsky <benjamin.widawsky@intel.com>
Date:   Sat Dec 28 13:31:49 2013 -0800

    drm/i915: set ctx->initialized only after RCS

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Damien Lespiau <damien.lespiau@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
[Jani: add reference to the earlier fix in the commit messsage.]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>