ARM: dts: am4372: Add emif node

Add node for TI AM4372 EMIF. Without this we get a warning with the
recent commit fabbe6df

 (ARM: OMAP: AM43xx hwmod: Add data for am43xx
emif hwmod).

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Tested-by: Felipe Balbi <balbi@ti.com>
Acked-by: Felipe Balbi <balbi@ti.com>
[tony@atomide.com: updated comments]
Signed-off-by: Tony Lindgren <tony@atomide.com>