The input clock and number of clock provider cells are not required for
the PMIC to operate.  They are needed only for the optional bd718x7
clock driver.

Add also clock-output-names as driver takes use of it.

This fixes dtbs_check warnings like:

    arch/arm64/boot/dts/freescale/imx8mn-ddr4-evk.dt.yaml: pmic@4b: 'clocks' is a required property
    arch/arm64/boot/dts/freescale/imx8mn-ddr4-evk.dt.yaml: pmic@4b: '#clock-cells' is a required property
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Signed-off-by: Rob Herring <robh@kernel.org>