dt-bindings: remoteproc: pru: Update bindings for 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, yet retaining some of the
features from AM65x SR1.0 like the PRU IRAM size etc. The ICSSG IP
on K3 AM65x SR2.0 SoCs have two new custom auxiliary PRU cores called
Transmit PRUs (Tx_PRUs) in addition to the existing PRUs and RTUs.

Update the PRU remoteproc bindings for these Tx PRU cores.

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