drm/i915: Consolidate reset_request()

Always reset the requests of the guilty context, including the hung
request that we tell the hardware to skip. This should help if the
reprogram fails entirely, but more importantly makes the guilty path
more uniform (and simplifies the subsequent patch to tweak the cancelled
requests).

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: http://patchwork.freedesktop.org/patch/msgid/20170110172246.27297-1-chris@chris-wilson.co.uk