dt-bindings: net: generalize moxart-mac to support all faraday based ftmac IP

Andestech and moxa use the same faraday mac IP, so we use faraday,ftmac.txt to
describe it.
Signed-off-by: Greentime Hu <green.hu@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/net/moxa,moxart-mac.txt → Documentation/devicetree/bindings/net/faraday,ftmac.txt

-MOXA ART Ethernet Controller
+Faraday Ethernet Controller
 
 Required properties:
 
-- compatible : Must be "moxa,moxart-mac"
+- compatible : Must contain "faraday,ftmac", as well as one of
+		the SoC specific identifiers:
+		"andestech,atmac100"
+		"moxa,moxart-mac"
 - reg : Should contain register location and length
 - interrupts : Should contain the mac interrupt number