dt-bindings: phy: mvebu-comphy: extend the file to describe a3700 bindings

Current file describe COMPHY bindings for the IP available on the
CP110 of Armada 7k/8k. Bindings are very close (and serve the same
purpose) as the new Armada 3700 COMPHY driver so update this file to
describe both. Also add an example of how to use this second
compatible (same as for the ESPRESSObin).

While doing so, enhance a bit the file by adding upper case where
needed.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>