ARM: dts: AM43x: Initial support

DT source (minimal) for AM4372 SoC to represent AM43x SoC's. Those
represented here are the minimal DT nodes necessary to get kernel
booting.

In DT nodes, "ti,hwmod" property has not been added, this would be
added along with PRCM support for AM43x.

Signed-off-by: Ankur Kishore <a-kishore@ti.com>
Signed-off-by: Afzal Mohammed <afzal@ti.com>
Signed-off-by: Benoit Cousson <benoit.cousson@linaro.org>