arm: am335x: Add DT (FDT) support to Siemens boards

Enable FDT support for all Siemens AM335x boards. To support
newer Linux kernels with DT booting.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Heiko Schocher <hs@denx.de>
Cc: Roger Meier <r.meier@siemens.com>
Cc: Lukas Stockmann <lukas.stockmann@siemens.com>
Cc: Tom Rini <trini@ti.com>
Acked-by: Heiko <Schocher&lt;hs@denx.de>