mb/google/fatcat: Allow board-specific FSP-M UPD override

This commit introduces a mechanism to allow mainboards to override
the default FSP-M UPDs for Panther Lake.

- Adds `variant_update_soc_memory_init_params` as a weak function
  in `variants.h` and `romstage.c` for board-specific implementations.
- In `romstage.c`, `mainboard_memory_init_params` now calls
  `variant_update_soc_memory_init_params` to apply board-specific
  overrides to the FSP-M UPDs.

This enables finer-grained control over memory initialization parameters
at the variant level.

BUG=b:328770565
TEST=Able to build and boot google/fatcat.

Change-Id: I403bc4270ef526363defa6cd7d22741ad42a8a76
Signed-off-by: Subrata Banik <subratabanik@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/87089
Reviewed-by: Sowmya Aralguppe <sowmya.aralguppe@intel.com>
Reviewed-by: Jayvik Desai <jayvik@google.com>
Reviewed-by: Pranava Y N <pranavayn@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/fatcat/romstage.c

@@ -3,6 +3,7 @@
 #include <baseboard/variants.h>
 #include <fsp/api.h>
 #include <soc/romstage.h>
+#include <soc/soc_chip.h>
 #include <string.h>
 
 /*
@@ -16,6 +17,11 @@ __weak void fw_config_configure_pre_mem_gpio(void)
 	/* Nothing to do */
 }
 
+__weak void variant_update_soc_memory_init_params(FSPM_UPD *memupd)
+{
+	/* Nothing to do */
+}
+
 void mainboard_memory_init_params(FSPM_UPD *memupd)
 {
 	const struct pad_config *pads;
@@ -33,4 +39,7 @@ void mainboard_memory_init_params(FSPM_UPD *memupd)
 	variant_get_spd_info(&spd_info);
 
 	memcfg_init(memupd, mem_config, &spd_info, half_populated);
+
+	/* Override FSP-M UPD per board if required. */
+	variant_update_soc_memory_init_params(memupd);
 }

src/mainboard/google/fatcat/variants/baseboard/include/baseboard/variants.h

@@ -4,6 +4,7 @@
 #define __BASEBOARD_VARIANTS_H__
 
 #include <chip.h>
+#include <fsp/api.h>
 #include <soc/gpio.h>
 #include <soc/meminit.h>
 #include <stdint.h>
@@ -23,6 +24,7 @@ const struct mb_cfg *variant_memory_params(void);
 void variant_get_spd_info(struct mem_spd *spd_info);
 int variant_memory_sku(void);
 bool variant_is_half_populated(void);
+void variant_update_soc_memory_init_params(FSPM_UPD *memupd);
 void variant_update_soc_chip_config(struct soc_intel_pantherlake_config *config);
 
 enum s0ix_entry {