Some platforms e.g. TI Davinci require 32-bit accesses to the UARTs.
The of_serial driver currently registers all UARTs as UPIO_MEM.  Add a
new attribute "reg-io-width" to allow the port to be registered with
different IO width requirements.
Acked-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NJamie Iles <jamie@jamieiles.com>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>