cpu/x86/lapic: Fix SMP=n case with LEGACY_SMP_INIT

Fix regression after commit 9ec7227c9b
  cpu/x86/lapic: Move LAPIC configuration to MP init

The call to disable_lapic() got removed and with asus/p2b
SeaBIOS payload was unable to load kernel.

The combination of entering SeaBIOS payload with an
enabled lapic but not having programmed LAPIC_LVT0
for DELIVERY_MODE_EXTINT apparently disconnects i8259
PIC interrupt delivery pin.

Change-Id: If51e5d65153a02ac7af191e7897c04bd4e298006
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/61793
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>

src/cpu/x86/lapic/lapic_cpu_init.c

@@ -384,6 +384,8 @@ void initialize_cpus(struct bus *cpu_bus)
 	if (is_smp_boot()) {
 		enable_lapic();
 		setup_lapic_interrupts();
+	} else {
+		disable_lapic();
 	}
 
 	/* Get the device path of the boot CPU */