platform/x86: intel_pmc_core: Refactor the driver by removing redundant code

pmc_core_slps0_dbg_show() is responsible for displaying debug registers
through slp_s0_debug_status entry. The driver uses the same but
redundant code to dump these debug registers for an S0ix failure.

Hence, refactor the driver by removing redundant code and reuse the
same function that both dumps registers through slp_s0_debug_status
entry and in resume for an S0ix failure.

The changes in this patch are preparatory, so platforms that support low
power sub-states can dump the debug registers when the attempt to enter
low power states are unsuccessful.

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