serial: core: Include console.h from serial_core.h

In the static inline function uart_handle_break() in serial_core.h we
dereference port->cons.  That gives an error unless console.h is also
included.

This error hasn't shown up till now because everyone who has defined
SUPPORT_SYSRQ has also included console.h, but it's a bit ugly to make
this requirement.  Let's make the include explicit.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>