intel/smm/gen1: Use smm_subregion()

Change-Id: I371ed41f485b3143e47f091681198d6674928897
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34740
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/include/cpu/intel/smm_reloc.h

@@ -23,8 +23,6 @@ struct ied_header {
 } __packed;
 
 /* These helpers are for performing SMM relocation. */
-u32 northbridge_get_tseg_base(void);
-u32 northbridge_get_tseg_size(void);
 void northbridge_write_smram(u8 smram);
 
 void smm_lock(void);