Several serial drivers want to obtain the numeric baud rate when
configuring their serial ports.  Currently, two methods are used
to "work around" this inadequacy in the change_speed API:

	baud = tty_get_baud_rate(port->info->tty);

	baud = BAUD_BASE / (16 * quot);

Passing the termios structure down means that we can use 
uart_get_baud_rate() instead.  We can also ensure that the various
termios flags for options we don't support are correctly set.

Lastly, this also provides 8250.c with a clean method for supporting
divisors that are greater than the baud_base.