platform/x86: intel_pmc_core: Convert to INTEL_CPU_FAM6 macro

INTEL_CPU_FAM6() macro provides better abstraction and reduces code size
so use it instead of custom grown ICPU().

Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>