dts: nrf/stm32: supress duplicate unit-address warning

A number of SoCs have overlapping devices at the same unit address.
Surpress the warning for those cases:

* NRF - kmu@39000 & flash-controller@39000
* NRF - clock@5000 & power@5000
* NRF - image@20000000 & image_s@20000000
* NRF - i2c@40003000 & spi@40003000
* STM - i2s@40003800 & spi@40003800

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>