cpu/qemu-x86: Drop select SMP

With MAX_CPUS==1, this has the effect of removing spinlock
implementation. But since is_smp_boot() evaluates false and
SMM uses separate smi_semaphore, there is no concurrency to
protect against with a spinlock.

Change-Id: I7c2ac221af78055879e7359bd03907f2416a9919
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/43865
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/cpu/qemu-x86/Kconfig

@@ -2,7 +2,6 @@
 
 config CPU_QEMU_X86
 	bool
-	select SMP
 	select UDELAY_TSC
 	select TSC_MONOTONIC_TIMER
 	select UNKNOWN_TSC_RATE