Documentation: devicetree: sja1000: add reg-io-width binding

Add the reg-io-width property to describe the width of the memory
accesses.

Cc: Grant Likely <grant.likely@linaro.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>
Cc: devicetree@vger.kernel.org
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Florian Vaussard <florian.vaussard@epfl.ch>
Tested-by: Andreas Larsson <andreas@gaisler.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

Documentation/devicetree/bindings/net/can/sja1000.txt

@@ -12,6 +12,10 @@ Required properties:
 
 Optional properties:
 
+- reg-io-width : Specify the size (in bytes) of the IO accesses that
+	should be performed on the device.  Valid value is 1, 2 or 4.
+	Default to 1 (8 bits).
+
 - nxp,external-clock-frequency : Frequency of the external oscillator
 	clock in Hz. Note that the internal clock frequency used by the
 	SJA1000 is half of that value. If not specified, a default value