platform/x86: intel_pmc_core: Add Intel Elkhart Lake support

Add Intel Elkhart Lake to the list of the platforms that driver supports
for the PMC device.

Just like Ice Lake and Tiger Lake, Elkhart Lake can also reuse all the
Cannon Lake PCH IPs. Also, it uses the same PCH IPs of Tiger Lake, no
additional effort is needed to enable but to simply reuse them.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Srinivas Pandruvada <srinivas.pandruvada@intel.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: David E. Box <david.e.box@intel.com>
Cc: Rajneesh Bhardwaj <irenic.rajneesh@gmail.com>
Cc: Tony Luck <tony.luck@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Gayatri Kammela <gayatri.kammela@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>