arm: mach-k3: invert logic for split DM firmware config

Currently, for the K3 generation of SoCs, there are more SoCs that
utilize the split firmware approach than the combined DMSC firmware.
Invert the logic to avoid adding more and more SoCs to this list.

Reviewed-by: Neha Malcom Francis <n-francis@ti.com>
Acked-by: Andrew Davis <afd@ti.com>
Signed-off-by: Bryan Brattlof <bb@ti.com>