ARM: shmobile: ape6evm: add DT reference

This patch adds a sample DT-based APE6EVM "reference" implementation. The
use of platform-specific C-code should be avoided with this configuration
as much as possible.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski+renesas@gmail.com>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>