x86/smm: Initialize SMM on some CPUs one-by-one

We currently race in SMM init on Atom 230 (and potentially
other CPUs). At least on the 230, this leads to a hang on
RSM, likely because both hyperthreads mess around with
SMBASE and other SMM state variables in parallel without
coordination. The same behaviour occurs with Atom D5xx.

Change it so first APs are spun up and sent to sleep, then
BSP initializes SMM, then every CPU, one after another.

Only do this when SERIALIZE_SMM_INITIALIZATION is set.
Set the flag for Atom CPUs.

Change-Id: I1ae864e37546298ea222e81349c27cf774ed251f
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Signed-off-by: Damien Zammit <damien@zamaudio.com>
Reviewed-on: https://review.coreboot.org/6311
Tested-by: build bot (Jenkins)
Tested-by: BSI firmware lab <coreboot-labor@bsi.bund.de>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/arch/x86/cpu.c

@@ -234,6 +234,9 @@ void cpu_initialize(unsigned int index)
 		die("CPU: missing cpu device structure");
 	}
 
+	if (cpu->initialized)
+		return;
+
 	post_log_path(cpu);
 
 	/* Find what type of cpu we are dealing with */