x86_64: write printk messages to COM1 serial port

arch/x86_64/init.c

@@ -12,6 +12,7 @@
 #include <socks/machine/cpu.h>
 #include <socks/libc/stdio.h>
 #include <arch/vgacon.h>
+#include <arch/serial.h>
 #include <arch/acpi.h>
 
 #define PTR32(x) ((void *)((uintptr_t)(x)))
@@ -47,6 +48,7 @@ int ml_init(uintptr_t arg)
 
 	bootstrap_cpu_init();
 	vgacon_init();
+	serialcon_init();
 	clock_calibrate(500);
 
 	print_kernel_banner();