ACPI: processor: Refactor arch_acpi_set_pdc_bits()

The capabilities buffer modified by the arch_acpi_set_pdc_bits() is not
_PDC-specific, as it can be used by _OSC too.

Change the name of that function to better reflect its independence from
_PDC and make it take the capabilities buffer address as the argument
directly, without any offset, as _OSC and _PDC use different capabilities
buffer offsets.

No intentional functional impact.

Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>