ARM: shmobile: Remove KZM9D reference DTS

Now when the legacy DTS file emev2-kzm9d.dts can be
used with board-kzm9d.c and board-kzm9d-reference.c
proceed with removing emev-kzm9d-reference.dts.

Signed-off-by: Magnus Damm <damm@opensource.se>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>