drm/i915/fbc: Add fbc tracepoints

Add tracepoints which let us know when fbc activates/deactivates/nukes.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191213133453.22152-5-ville.syrjala@linux.intel.com


Reviewed-by: Imre Deak <imre.deak@intel.com>