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/soc/intel/broadwell/pch/lpc.c

@@ -616,7 +616,8 @@ static void southcluster_inject_dsdt(const struct device *device)
 		return;
 
 	soc_fill_gnvs(gnvs);
-	acpi_create_gnvs(gnvs);
+	mainboard_fill_gnvs(gnvs);
+
 	acpi_inject_nvsa();
 }