Platform/DeveloperBox: drop dma-ranges property from DT root node

The dma-ranges DT property describes the DMA translation between a
parent bus and its children, and so having a dma-ranges property in
the root node makes little sense, but it doesn't harm either.

However, recent kernels (v5.5+) have started spewing warnings into
the kernel log of the following nature:

  OF: translation of DMA address(0) to CPU address failed node(/uart@2a400000)
  OF: translation of DMA address(0) to CPU address failed node(/pmu)
  OF: translation of DMA address(0) to CPU address failed node(/pcie@60000000)
  OF: translation of DMA address(0) to CPU address failed node(/pcie@60000000)
  OF: translation of DMA address(0) to CPU address failed node(/pcie@60000000)
  OF: translation of DMA address(0) to CPU address failed node(/pcie@60000000)
  OF: translation of DMA address(0) to CPU address failed node(/pcie@60000000)
  OF: translation of DMA address(0) to CPU address failed node(/pcie@60000000)
  OF: translation of DMA address(0) to CPU address failed node(/pcie@70000000)
  OF: translation of DMA address(0) to CPU address failed node(/uart@51040000)
  OF: translation of DMA address(0) to CPU address failed node(/gpio@51000000)
  OF: translation of DMA address(0) to CPU address failed node(/i2c@51210000)
  OF: translation of DMA address(0) to CPU address failed node(/gpio-keys)
  OF: translation of DMA address(0) to CPU address failed node(/tpm_tis@10000000)
  OF: translation of DMA address(0) to CPU address failed node(/sdhci@52300000)
  OF: translation of DMA address(0) to CPU address failed node(/ethernet@522d0000)
  OF: translation of DMA address(0) to CPU address failed node(/pcie@60000000)
  OF: translation of DMA address(0) to CPU address failed node(/pcie@60000000)

and so we should probably get rid of this bogus dma-ranges property.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>