TTY: serial, fix includes in some drivers

linux/tty_flip.h is included in linux/serial_core.h. But this may (and
will) change in the future. Then we would get build errors such as:
.../tty/serial/max3107.c: In function ‘put_data_to_circ_buf’:
.../tty/serial/max3107.c:149:2: error: implicit declaration of function ‘tty_insert_flip_string’

So fix all the drviers which call tty flip buffer helpers to really
include linux/tty_flip.h. And also make sure that those include
linux/tty.h when operating with struct tty_struct.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/drivers/tty/serial/mux.c b/drivers/tty/serial/mux.c
index 9711e06..06f6aef 100644
--- a/drivers/tty/serial/mux.c
+++ b/drivers/tty/serial/mux.c
@@ -21,6 +21,8 @@
 #include <linux/ioport.h>
 #include <linux/init.h>
 #include <linux/serial.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
 #include <linux/console.h>
 #include <linux/delay.h> /* for udelay */
 #include <linux/device.h>