drm/i915/execlists: Ensure the context is reloaded after a GPU reset

After we manipulate the context to allow replay after a GPU reset, force
that context to be reloaded. This should be a layer of paranoia, for if
the GPU was reset, the context will no longer be resident!

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Acked-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190912092933.4729-2-chris@chris-wilson.co.uk