Now when CCF is supported remove the legacy KZM9D reference
Kconfig bits CONFIG_MACH_KZM9D_REFERENCE for the non-multiplatform
case.

Starting from this commit KZM9D board support is always enabled
via CONFIG_MACH_KZM9D, and CONFIG_ARCH_MULTIPLATFORM is used
to select between board-kzm9d.c and board-kzm9d-reference.c

The file board-kzm9d-reference.c can no longer be used together
with the legacy sh-clk clock framework, instead CCF is used.
Signed-off-by: NMagnus Damm <damm@opensource.se>
Acked-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>