tty: amba-pl011: add support for 32-bit register access

Add support for 32-bit register accesses to the AMBA PL011 UART.  This
is needed for ZTE UARTs, which require 32-bit accesses as opposed to
the more normal 16-bit accesses.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>