arm: mvebu: Reduce reg-io-width with UARTs

Setting the reg-io-width to 1 byte represents more accurate
description of the HW.

This will fix an issue where UART driver causes kernel
panic during bootup. Gregory CLEMENT traced the issue to
autoconfig() in 8250.c, where the existence of FIFO is
checked from UART_IIR register. The register is now read as
32-bit value as the reg-io-width is set to 4-bytes. The
retuned value seems to contain bogus data for bits 31:8,
causing the issue.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: Gregory CLEMENT <gregory.clement@free-electrons.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Tested-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Tested-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>