remoteproc/pru: Add support for Tx PRU cores on K3 AM65x SR2.0 SoCs

The AM65x SR2.0 SoCs have a revised ICSSG IP that is based off the
subsequent IP revision used on J721E SoCs. This IP instance has two
new custom auxiliary PRU cores called Transmit PRUs (Tx_PRUs) in
addition to the existing PRUs and RTUs.

The Tx_PRU cores have their own dedicated IRAM (smaller than a PRU
or RTY), Control and debug feature sets. The RTU and Tx_PRU cores
though share the same Data RAMs as the PRU cores, so the memories
have to be partitioned carefully between different applications.

Enhance the existing PRU remoteproc driver to support these new Tx
PRU cores by using specific compatibles.

Signed-off-by: Suman Anna <s-anna@ti.com>