x86/lapic: Use the existing lapicid() function

coreboot has a lapicid() function, so use it.

Change-Id: I7f536c229f271674c34d722b5db96ce665b720f1
Signed-off-by: Marc Jones <marcj303@gmail.com>
Reviewed-on: https://review.coreboot.org/22192
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/cpu/x86/lapic/lapic_cpu_init.c

@@ -351,7 +351,7 @@ void stop_this_cpu(void)
 	unsigned long send_status;
 	unsigned long id;
 
-	id = lapic_read(LAPIC_ID) >> 24;
+	id = lapicid();
 
 	printk(BIOS_DEBUG, "CPU %ld going down...\n", id);