platform/x86: intel_pmc_core: Read base address from LPIT

Read SLP_S0 address from ACPI LPIT table when present and use PMC
specific SLP_S0 offset to get the base address of PMC MMIO.

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