ARM: shmobile: ape6evm-reference: Remove board C code and DT file

Now that the r8a73a4 generic multiplatform case has the same features as the
APE6EVM DT reference board code, we get rid of the latter.  DT reference
code in the future shall make use of the r8a73a4 multiplatform support code
with the generic SoC machine vector.

Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
Acked-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
[geert: Update Documentation/devicetree/bindings/arm/shmobile.txt]
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>