cpu/x86/mp_init: retype do_smm element in mp_state struct to bool

The do_smm struct element in the mp_state struct was an int even though
it only had two possible states, so change it to bool to make this more
obvious. Also change the return type of is_smm_enabled from int to bool.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I8d2d95f0497649d67565243d14a5ab9c9cdda412
Reviewed-on: https://review.coreboot.org/c/coreboot/+/65776
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/security/intel/stm/SmmStm.c

@@ -72,7 +72,7 @@ extern struct mp_state {
 	uintptr_t perm_smbase;
 	size_t perm_smsize;
 	size_t smm_save_state_size;
-	int do_smm;
+	bool do_smm;
 } mp_state;
 
 typedef union {