RK3588 Audio Support

Merge series from Nicolas Frattaroli <frattaroli.nicolas@gmail.com>:

This patchset refactors the Rockchip I2S/TDM driver in order to
support the RK3588 SoC, and then adds the necessary compatible
string to load the driver for it.

Patch 1 rectifies a problem with the bindings where we were too
strict about requiring the rockchip,grf property. Most features
of this audio device don't need access to the GRF to function.

Patch 2 modifies the driver to adjust its behaviour to what the
changed bindings now allow, namely using most things without the
GRF.

Patch 3 and 4 are boring compatible string stuff that enables
RK3588 support. No special data is needed to initialise the
driver for this instance of the I2S/TDM IP.