broadwell: Drop weak mainboard_fill_spd_data definition

Make `mainboard_fill_spd_data` mandatory and adapt mainboards to define
this function accordingly.

Change-Id: Ic18c4c574e8c963bbb41c980f43bdbacc57735af
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55806
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/broadwell/raminit.c

@@ -177,10 +177,6 @@ static void setup_sdram_meminfo(struct pei_data *pei_data)
 	}
 }
 
-__weak void mainboard_fill_spd_data(struct pei_data *pei_data)
-{
-}
-
 void perform_raminit(const struct chipset_power_state *const power_state)
 {
 	const int s3resume = power_state->prev_sleep_state == ACPI_S3;