tcl/target/ti_k3: Introduce RTOS array variable to set various CPU RTOSes

tcl/target/ti_k3: Introduce RTOS array variable to set various CPU RTOSes

The Texas Instruments' K3 devices are a mix of AMP and SMP systems.
The operating systems used on these processors can vary dramatically
as well. Introduce a RTOS array variable, which is keyed off the cpu
to identify which RTOS is used on that CPU. This can be "auto" or
"hwthread" in case of SMP debug etc.

For example:
AM625 with an general purpose M4F running Zephyr and 4 A53s running SMP
Linux could be invoked by:
openocd -c 'set V8_SMP_DEBUG 1' -c 'set RTOS(am625.cpu.gp_mcu) Zephyr' \
	-c "set RTOS(am625.cpu.a53.0) hwthread" -f board/ti_am625evm.cfg

Change-Id: Ib5e59fa2583b3115e5799658afcdd0ee91935e82
Reported-by: Dubravko Srsan <dubravko.srsan@dolotron.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/7898
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>