drivers: nxp,rtxxx-dsp-ctl: Extend to mimxrt798s/hifi4

Rework the driver so that it can cover multiple variants. Add variant DT
bindings. Change the compatible name for the mimxrt685s/cm33 DT.

This needed to be done because the hardware initialisation routines
(power, clocks, ...) are different from mimxrt685s/hifi4 to
mimxrt798s/hifi4. The same is expected for the /hifi1 domain.

Signed-off-by: Vit Stanicek <vit.stanicek@nxp.com>