mb/x/acpi_tables: Rename to mainboard_fill_gnvs()

Rename acpi_create_gnvs() functions under mb/ to reflect
their changed functionality.

Remove now empty mb/acpi_tables.c files.

Change-Id: Ia366867ef73d1ade9805dc29b8e14b3073f44f60
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/48707
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/acpi/gnvs.c

@@ -36,6 +36,7 @@ __weak uint32_t *gnvs_cbmc_ptr(struct global_nvs *gnvs_)
 }
 
 __weak void soc_fill_gnvs(struct global_nvs *gnvs_) { }
+__weak void mainboard_fill_gnvs(struct global_nvs *gnvs_) { }
 
 void *gnvs_get_or_create(void)
 {