ACPI: DPTF: Add PCH FIVR participant driver

This driver adds support for Dynamic Platform and Thermal Framework
(DPTF) PCH (Platform Controller Hub) FIVR (Fully Integrated Voltage
Regulator) participant support.

This participant is responsible for exposing platform telemetry and
control for:
	freq_mhz_high_clock
	freq_mhz_low_clock

These attributes are used to get and set PCH FIVR switching frequency
for thermal and radio frequency interference mitigation.

Refer to Documentation/ABI/testing/sysfs-platform-dptf for ABI details.

ACPI methods description used in this driver:
RFC0: This ACPI method to set PCH FIVR switching frequency when FIVR
clock is 19.2MHz or 24MHz. The ACPI method takes a DWORD value.
GFC0: This ACPI method to get PCH FIVR switching frequency when FIVR
clock is 19.2MHz or 24MHz.
RFC1: This ACPI method to set PCH FIVR switching frequency when FIVR
clock is 38.4MHz. The ACPI method takes a DWORD value.
GFC1: This ACPI method to get PCH FIVR switching frequency when FIVR
clock is 38.4MHz.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>