cpu/x86: Move smm_lock() prototype

The function implementations are in local platform
scopes.

Change-Id: I7a3025398b15fe6d2c5a13cdb65f3e62a49c0bc6
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34151
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/arch/x86/include/arch/cpu.h

@@ -203,9 +203,10 @@ static inline unsigned int cpuid_edx(unsigned int op)
 unsigned int cpu_cpuid_extended_level(void);
 int cpu_have_cpuid(void);
 
+/* Only with !PARALLEL_MP. */
 void smm_init(void);
 void smm_init_completion(void);
-void smm_lock(void);
+
 void smm_setup_structures(void *gnvs, void *tcg, void *smi1);
 
 static inline bool cpu_is_amd(void)