drivers: i2s: Add support for nRF I2S peripherals

Add a shim that allows using the nrfx I2S driver via the Zephyr API.
Add also missing devicetree nodes representing the I2S peripherals
in the nRF52 Series SoCs.
Extend the "nordic,nrf-i2s" binding with a new property that allows
specifying the clock source to be used by the I2S peripheral (so that
it is possible to use HFXO for better accurracy of the peripheral clock
or, in the nRF53 Series SoCs, to use the dedicated audio oscillator).

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>