bus: ti: add minimal sysc interconnect target driver

We can handle the sysc interconnect target module in a generic way for
many TI SoCs. Initially let's just enable domain clocks before the
children are probed.

The code is loosely based on the drivers/bus/ti-sysc.c of the Linux
kernel version 5.9-rc7.
For DT binding details see:
- Documentation/devicetree/bindings/bus/ti-sysc.txt

Signed-off-by: Dario Binacchi <dariobin@libero.it>