tty: serial: fsl_lpuart: add 32-bit register interface support

This add the 32-bit register version LPUART support with big-endian
byte order.
Signed-off-by: NJingchang Lu <jingchang.lu@freescale.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>