Use DT_MACHINE_START() on the sh73a0 based KZM9G board.

Also include a tiny DTS file to describe the board and
update the Kconfig dependencies to select CONFIG_USE_OF.
Signed-off-by: NMagnus Damm <damm@opensource.se>
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>

Add generic DT board support for the sh7372 SoC V2.

SCIF serial ports and timers are kept as regular
platform devices. Other on-chip and on-board devices
should be configured via the device tree.

Tested on the mackerel board via kexec using a zImage
kernel with an appended dtb.

At this point there is no interrupt controller support
in place but such code will be added over time when
proper IRQ domain support has been added to INTC.
Signed-off-by: NMagnus Damm <damm@opensource.se>
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>