drm/i915: Mark per-engine-reset as supported on gen7

The benefit of only resetting a single engine is that we leave other
streams of userspace work intact across a hang; vital for process
isolation. We had wired up individual engine resets for gen6, but only
enabled it from gen8; now let's turn it on for the forgotten gen7. gen6
is still a mystery as how to unravel some global state that appears to
be reset along with an engine (in particular the ppgtt enabling in
GFX_MODE).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210119110802.22228-6-chris@chris-wilson.co.uk