Add a shim that allows using the nrfx PDM driver via the Zephyr API.
Add also missing devicetree nodes representing the PDM peripherals
in the nRF52 Series SoCs.
Extend the "nordic,nrf-pdm" binding with a new property that allows
specifying the clock source to be used by the PDM peripheral (so that
it is possible to use HFXO for better accuracy 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>
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