platform/x86: intel_pmc_core: Add debugfs entry for low power mode status registers

Tiger Lake has 6 status registers that are memory mapped. These
registers show the status of the low power mode requirements. The
registers are latched on every C10 entry or exit and on every s0ix.y
entry/exit. Accessing these registers is useful for debugging any low
power related activities.

Thus, add debugfs entry to access low power mode status registers.

Cc: Srinivas Pandruvada <srinivas.pandruvada@intel.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: David Box <david.e.box@intel.com>
Signed-off-by: David Box <david.e.box@intel.com>
Signed-off-by: Gayatri Kammela <gayatri.kammela@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>