tty: serial: fsl_lpuart: Simplify RX/TX IRQ handlers

tty: serial: fsl_lpuart: Simplify RX/TX IRQ handlers

It appears that lpuart_rxint, lpuart_txint and lpuart32_rxint were
modelled after identical function found in UART driver for
i.MX. However, while said functions are used as individual IRQ
handlers in i.MX driver (in case of i.MX1), it is not the case for
LPUART. Given that, there's no need for us to restrict the prototype
of the handler to irqreturn_t foo(int, void *) and we can drop all of
uneened boilerplate code by changing it void foo(struct lpuart_port *).

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: Stefan Agner <stefan@agner.ch>
Cc: Bhuvanchandra DV <bhuvanchandra.dv@toradex.com>
Cc: Chris Healy <cphealy@gmail.com>
Cc: Cory Tusar <cory.tusar@zii.aero>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: linux-imx@nxp.com
Cc: linux-serial@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Link: https://lore.kernel.org/r/20190729195226.8862-5-andrew.smirnov@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>