soc/intel/alderlake: Default to 512 for DIMM_SPD_SIZE

Alderlake and Raptorlake SoCs support DDR4 and DDR5, which have a total
SPD size of 512 bytes. Set this as the default and remove the setting
from mainboard Kconfigs.

Change-Id: I8703ec25454a0cd55a3de70f73d2117285a833ae
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82115
Reviewed-by: Eric Lai <ericllai@google.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/alderlake/Kconfig

@@ -146,6 +146,9 @@ config SOC_INTEL_RAPTORLAKE_PCH_S
 
 if SOC_INTEL_ALDERLAKE
 
+config DIMM_SPD_SIZE
+	default 512
+
 config SOC_INTEL_ALDERLAKE_TCSS_USB4_SUPPORT
 	bool
 	default n if SOC_INTEL_ALDERLAKE_PCH_S