ARM: dts: split am335x-baltos-ir5221 into dts and dtsi files

Introduce am335x-baltos.dtsi, that provides common configuration
for the whole device family based on the same SODIMM module.
Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>