TTY: pty, switch to tty_alloc_driver

Switch to the new driver allocation interface, as this is one of the
special call-sites. Here, we need TTY_DRIVER_DYNAMIC_ALLOC to not
allocate tty_driver->ports, cdevs and potentially other structures
because we reserve too many lines in pty. Instead, it provides the
tty_port<->tty_struct link in tty->ops->install already.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/include/linux/tty_driver.h b/include/linux/tty_driver.h
index 3adc362..1a85f00 100644
--- a/include/linux/tty_driver.h
+++ b/include/linux/tty_driver.h
@@ -391,6 +391,9 @@
  *	the requested timeout to the caller instead of using a simple
  *	on/off interface.
  *
+ * TTY_DRIVER_DYNAMIC_ALLOC -- do not allocate structures which are
+ *	needed per line for this driver as it would waste memory.
+ *	The driver will take care.
  */
 #define TTY_DRIVER_INSTALLED		0x0001
 #define TTY_DRIVER_RESET_TERMIOS	0x0002
@@ -398,6 +401,7 @@
 #define TTY_DRIVER_DYNAMIC_DEV		0x0008
 #define TTY_DRIVER_DEVPTS_MEM		0x0010
 #define TTY_DRIVER_HARDWARE_BREAK	0x0020
+#define TTY_DRIVER_DYNAMIC_ALLOC	0x0040
 
 /* tty driver types */
 #define TTY_DRIVER_TYPE_SYSTEM		0x0001