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

"simple-mfd" as standalone compatible is frowned upon, so model DMSS
(Data Movement Subsystem) node as simple-bus as there is really no need
for these nodes to be MFD.

Link: https://lore.kernel.org/r/20231005151302.1290363-2-vigneshr@ti.com
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>