tty: serial: lpuart: add little endian 32 bit register support

tty: serial: lpuart: add little endian 32 bit register support

Use standard port->iotype to distinguish endian difference. Note as we
read/write register by checking iotype dynamically, we need to initialize
the iotype correctly for earlycon as well to avoid a break.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com> (supporter:TTY LAYER)
Cc: Stefan Agner <stefan@agner.ch>
Cc: Mingkai Hu <Mingkai.Hu@nxp.com>
Cc: Yangbo Lu <yangbo.lu@nxp.com>
Cc: Fugang Duan <fugang.duan@nxp.com>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
ChangeLog:
v3->v4:
 * Removed unneeded semicolon catched by 0day Robot.
v2->v3:
 * Instead of using global var, use standard port->iotype to distinguish
   endian difference.
v1->v2:
 * No changes
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>