Kernel/init: /dev/tty is now custom symlink to controlling terminal

kernel now passes the name of default console to init process so init
knows which file to open as stdio. before /dev/tty was referencing the
system wide current terminal which was inherited from cmdline. This
doesn't work anymore as we have pseudo terminals implemented that can
chage the current terminal during runtime :D

kernel/include/kernel/Process.h

@@ -185,7 +185,7 @@ namespace Kernel
 
 		BAN::ErrorOr<long> sys_load_keymap(const char* path);
 
-		TTY& tty() { ASSERT(m_controlling_terminal); return *m_controlling_terminal; }
+		BAN::RefPtr<TTY> controlling_terminal() { return m_controlling_terminal; }
 
 		static Process& current() { return Thread::current().process(); }