ACPI / PMIC: intel: add REGS operation region support

At least some of the Broxtons have a third custom OpRegion
named REGS. This adds handling for it.

Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>