drm/i915/gt: Consolidate the CS timestamp clocks

Pull the GT clock information [used to derive CS timestamps and PM
interval] under the GT so that is it local to the users. In doing so, we
consolidate the two references for the same information, of which the
runtime-info took note of a potential clock source override and scaling
factors.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201223122359.22562-2-chris@chris-wilson.co.uk

drm/i915/gt: Use the RPM config register to determine clk frequencies

For many configuration details within RC6 and RPS we are programming
intervals for the internal clocks. From gen11, these clocks are
configuration via the RPM_CONFIG and so for convenience, we would like
to convert to/from more natural units (ns).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Andi Shyti <andi.shyti@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Andi Shyti <andi.shyti@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200424162805.25920-2-chris@chris-wilson.co.uk