init: Initialize serial subsystem before init_earlyinitcalls()

Otherwise, the serial sybsystem isn't initialized before the serial
drivers attempt to register themselves.

kernel/start_kernel.c

@@ -64,8 +64,9 @@ void serial_console_init() {
 		print_init(sdev->putc);
 }
 
+void serial_init();
 void kmalloc_init();
- 
+
 int main(void) {
 	char *lower, *upper;
 	struct atag *atags;
@@ -73,8 +74,13 @@ int main(void) {
 	//setup MMU
 	mmu_reinit();
 
+	/* Initialize the serial subsystem before
+	 * init_earlyinitcalls(), because console drivers get
+	 * initialized here so as to have an output console as
+	 * early as possible, and we don't want those
+	 * initializations to fail. */
+	serial_init();
 	init_earlyinitcalls();
-
 	serial_console_init();
 
 	//setup memory