arm64: dts: ti: k3-am65-mcu: add system control module node

The MCU System control module support is added to the device tree to allow
drivers to access to their System control module registers.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>