ACPI / CPPC: Check for valid PCC subspace only if PCC is used

Changes the behavior where we return error if there are no valid PCC
subspace for a given performance domain.

The ACPI spec does not mandate the use PCC, so it is possible to have
platforms where a PCC subspace may not be present, so we need to check
for a valid PCC subspace ID only if the register is a PCC register.

Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>