platform/x86: intel_pmc_core: Convert to a platform_driver

Convert the intel_pmc_core driver to a platform driver. There is no
functional change to the driver, or to the way the devices are
instantiated.

Signed-off-by: Rajat Jain <rajatja@google.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>