drm/i915/gt: Reuse the tasklet priority for virtual as their siblings

In order to keep all the tasklets in the same execution lists and so
fifo ordered, be consistent and use the same priority for all.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200518081440.17948-3-chris@chris-wilson.co.uk