drm/i915/gt: Show engine properties in the pretty printer

When debugging the engine state, include the user properties that may,
or may not, have been adjusted by the user/test.

For example,
vecs0
	...
	Properties:
		heartbeat_interval_ms: 2500 [default 2500]
		max_busywait_duration_ns: 8000 [default 8000]
		preempt_timeout_ms: 640 [default 640]
		stop_timeout_ms: 100 [default 100]
		timeslice_duration_ms: 1 [default 1]

Suggested-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200916090059.3189-1-chris@chris-wilson.co.uk