Support for multiple (3) console= on kernel cmdline

Some targets, like Raspberry Pi, have both serial and HDMI console
enabled.  Depending on the order of arguments on the kernel cmdline
either one were selected the default 'stderr', which finit used.

This patch adds support for parsing the console= string(s) and
opening multiple outputs for system startup/progress.  In the
end, however, a getty still needs to be started on each of the
consoles to use.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/helpers.h

@@ -50,6 +50,9 @@ void          endfsent  (void);
 struct fstab *getfsent  (void);
 #endif	/* HAVE_GETFSENT */
 
+void    add_console     (char *str);
+ssize_t cprintf         (const char *fmt, ...);
+
 char   *strip_line      (char *line);
 
 int     getty           (char *tty, speed_t speed, char *term, char *user);