platform/x86: intel_pmc_core: Change driver to a module

Allow the driver to be a module since builtin_pci_driver funtionality is no
longer needed.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>