soc/intel: Make use of PMC low power program from common block

List of changes:
1. Select PMC_LOW_POWER_MODE_PROGRAM from applicable SoC directory
2. Remove redundant PMC programming from SoC and refer to common
code block
3. Remove unused 'reg8' and 'reg32' variable as applicable from SoC
function.

Change-Id: I18894c49cfc6e88675b5fb71bca0412e5639fb4b
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/45796
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/icelake/Kconfig

@@ -30,6 +30,7 @@ config CPU_SPECIFIC_OPTIONS
 	select FSP_PEIM_TO_PEIM_INTERFACE
 	select REG_SCRIPT
 	select PMC_GLOBAL_RESET_ENABLE_LOCK
+	select PMC_LOW_POWER_MODE_PROGRAM
 	select CPU_INTEL_COMMON_SMM
 	select SOC_INTEL_COMMON
 	select SOC_INTEL_COMMON_ACPI_WAKE_SOURCE