dt-bindings: ARM: add bindings for the Meraki MR32

mark the Meraki MR32 and its SoC (BCM53016) as supported
in the bindings documentation file.

A quick look on Broadcom BCM5301x series umbrella website reveals:

<https://www.broadcom.com/products/embedded-and-networking-processors/communications/bcm5301x

>

"BCM53012 and BCM53016 with dual-core Cortex-A9 CPU at 1 GHz, 256KB L2 cache,
 16-bit DDR2 interface, USB3 integrated switch, GPHYs and packet accelerator".

As far as I can tell, Broadcom considers the SoC to be
a version of the BCM53012.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Acked-by: Scott Branden <scott.branden@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>