ACPI: CPPC: Check _OSC for flexible address space

ACPI 6.2 Section 6.2.11.2 'Platform-Wide OSPM Capabilities':
  Starting with ACPI Specification 6.2, all _CPC registers can be in
  PCC, System Memory, System IO, or Functional Fixed Hardware address
  spaces. OSPM support for this more flexible register space scheme is
  indicated by the “Flexible Address Space for CPPC Registers” _OSC bit

Otherwise (cf ACPI 6.1, s8.4.7.1.1.X), _CPC registers must be in:
- PCC or Functional Fixed Hardware address space if defined
- SystemMemory address space (NULL register) if not defined

Add the corresponding _OSC bit and check it when parsing _CPC objects.

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>