ACPI: processor: Rename ACPI_PDC symbols

The prefix in the names of the ACPI_PDC symbols suggests that they are
only relevant for _PDC, but in fact they can also be used in the _OSC.

Change that prefix to a more generic ACPI_PROC_CAP that will better
reflect the purpose of those symbols as they represent bits in a general
processor capabilities buffer.

Rename pdc_intel.h to proc_cap_intel.h to follow the change of the
symbol name prefix.

No intentional functional impact.

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