soc/intel/alderlake: Introduce PCH-S symbol

Introduce SOC_INTEL_ALDERLAKE_PCH_S symbol to differentiate from the
low power chipsets.

Signed-off-by: Michał Żygowski <michal.zygowski@3mdeb.com>
Change-Id: I47676723747458b8b7fe726e900843c198901bda
Reviewed-on: https://review.coreboot.org/c/coreboot/+/63455
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/soc/intel/alderlake/Kconfig

@@ -23,6 +23,12 @@ config SOC_INTEL_ALDERLAKE_PCH_P
 	help
 	  Choose this option if your mainboard has a PCH-P chipset.
 
+config SOC_INTEL_ALDERLAKE_PCH_S
+	bool
+	select SOC_INTEL_ALDERLAKE
+	help
+	  Choose this option if your mainboard has a PCH-S chipset.
+
 if SOC_INTEL_ALDERLAKE
 
 config CPU_SPECIFIC_OPTIONS