Add a DT reference implementation for the KZM9D board.

Only DT devices are used in this case. UART, STI, GPIO
and SMP / GIC are all provided by emev2.dtsi.

There is still a board specific C file used for enabling
legacy SH clocks. This file will be removed after we have
moved over to common clocks.
Signed-off-by: NMagnus Damm <damm@opensource.se>
[horms+renesas@verge.net.au: Do not include trailing blank line in
 board-kzm9d-reference.c ]
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>