drm/i915/gt: Trace RPS events

Add tracek to the RPS events (interrupts, worker, enabling, threshold
selection, frequency setting), so that if we have to debug reticent HW
we have some traces to start from.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Andi Shyti <andi.shyti@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200424162805.25920-1-chris@chris-wilson.co.uk