arm64: dts: ti: k3-*: Convert NAVSS to simple-bus

"simple-mfd" as standalone compatible is frowned upon, so model main and
MCU NAVSS (Navigator SubSystem) nodes as simple-bus as there is really
no need for these nodes to be MFD.

Link: https://lore.kernel.org/r/20231005151302.1290363-3-vigneshr@ti.com
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>