Previously we hesitated in adding the hw probe for the actual GPU
frequency for rps_boost as it is quite cumbersome, but given some
surprising HW behaviour it would be useful to know both the RPS boost
state and the actual HW state in one location.

v2: vlv/chv needs more tlc
Reported-by: NTomi Sarvela <tomi.p.sarvela@intel.com>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Reviewed-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181002113221.29208-1-chris@chris-wilson.co.uk