ARM: dts: am335x: add common dtsi for MOXA UC-8100 series

Add am335x-moxa-uc-8100-common.dtsi for many products of MOXA UC-8100
series, and remove common nodes from am335x-moxa-uc-8100-me-t.dts.
Signed-off-by: Johnson Chen <johnsonch.chen@moxa.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>