ACPI / LPSS: add support for Intel BayTrail

Intel BayTrail has almost the same Low Power Subsystem than Lynxpoint with
few differences. Peripherals are clocked with different speeds (typically
lower) and the clock is not always gated. To support this we add
possibility to share a common fixed rate clock and make clock gating
optional.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>