ARM: dts: move aliases back to .dts in Cygnus

Move aliases from bcm-cygnus.dtsi back to individual .dts files. Also
clean up the chosen node to have the stdout-path using the proper alias

Signed-off-by: Ray Jui <rjui@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>