ARM: mach-shmobile: Use DT_MACHINE for mackerel

Use DT_MACHINE_START() on the sh7372 based mackerel board.

Also include a tiny DTS file to describe the board and update the
Kconfig dependencies to select CONFIG_USE_OF.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: Simon Horman <horms@verge.net.au>
diff --git a/arch/arm/mach-shmobile/board-mackerel.c b/arch/arm/mach-shmobile/board-mackerel.c
index 0c27c81..39b8f2e 100644
--- a/arch/arm/mach-shmobile/board-mackerel.c
+++ b/arch/arm/mach-shmobile/board-mackerel.c
@@ -1651,7 +1651,12 @@
 	pm_clk_add(&hdmi_lcdc_device.dev, "hdmi");
 }
 
-MACHINE_START(MACKEREL, "mackerel")
+static const char *mackerel_boards_compat_dt[] __initdata = {
+	"renesas,mackerel",
+	NULL,
+};
+
+DT_MACHINE_START(MACKEREL_DT, "mackerel")
 	.map_io		= sh7372_map_io,
 	.init_early	= sh7372_add_early_devices,
 	.init_irq	= sh7372_init_irq,
@@ -1659,4 +1664,5 @@
 	.init_machine	= mackerel_init,
 	.init_late	= sh7372_pm_init_late,
 	.timer		= &shmobile_timer,
+	.dt_compat  = mackerel_boards_compat_dt,
 MACHINE_END