remoteproc: k3-dsp: Extend support for C71x DSPs on J721S2 SoCs

The K3 J721S2 SoCs have two C71x DSP subsystems in MAIN voltage domain,
and there are no C66x DSP subsystems on these SoCs. The C71x DSP subsystem
is a slighly updated version of the C71x DSP subsystem on J721e. The
C71x DSPs are 64 bit machine with fixed and floating point DSP
operations.

Extend support to the C71x DSPs with J721S2 compatible strings.

Signed-off-by: Hari Nagalla <hnagalla@ti.com>