hvc_console: Add tty driver flag TTY_DRIVER_RESET_TERMIOS

After a tty hangup() or close() operation, processes might not reset the
termio settings to a sane state. In order to reset the termios to its
default settings the tty driver flag TTY_DRIVER_RESET_TERMIOS has been added.

TTY driver flag description from include/linux/tty_driver.h:
	TTY_DRIVER_RESET_TERMIOS --- requests the tty layer to reset the
	  termios setting when the last process has closed the device.
	  Used for PTY's, in particular.

Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>