ARM: dts: AM4372: Add the wkupm3 rproc node

Add the Wakeup M3 remote processor device node for
the AM4372 SoC. The WkupM3 remote processor is used
to implement and achieve low-power functionality on
the AM33xx & AM43xx SoCs.

This node is added as a child of the recently added
l4_wkup node to reflect its presence within the SoC.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>