sb/intel: Factor out soc_fill_gnvs()

Name the common part of GNVS initialisation as soc_fill_gnvs().
It is also moved before the call to acpi_create_gnvs(), which
followup will rename to mainbord_fill_gnvs() to reflect that
implementation is under mb/.

Change-Id: Ic4cf1548b65a86212d6e45d460fcd23bb8036365
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/48706
Reviewed-by: Lance Zhao
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/acpi/gnvs.c

@@ -35,6 +35,8 @@ __weak uint32_t *gnvs_cbmc_ptr(struct global_nvs *gnvs_)
 	return NULL;
 }
 
+__weak void soc_fill_gnvs(struct global_nvs *gnvs_) { }
+
 void *gnvs_get_or_create(void)
 {
 	size_t gnvs_size;