drivers/serial: add GENERIC_HARDIRQS dependency

Since SERIAL_CORE needs GENERIC_HARDIRQS (see below) and most serial drivers
select it, just add a GENERIC_HARDIRQS dependency to all serial drivers.

Fixes the compile error below:

drivers/tty/serial/serial_core.c: In function ‘uart_set_info’:
drivers/tty/serial/serial_core.c:725:2: error: implicit declaration of function ‘irq_canonicalize’

Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>