riscv: dts: starfive: Add pool for coherent DMA memory on JH7100 boards

riscv: dts: starfive: Add pool for coherent DMA memory on JH7100 boards

The StarFive JH7100 SoC has non-coherent device DMAs, but most drivers
expect to be able to allocate coherent memory for DMA descriptors and
such. However on the JH7100 DDR memory appears twice in the physical
memory map, once cached and once uncached:

  0x00_8000_0000 - 0x08_7fff_ffff : Off chip DDR memory, cached
  0x10_0000_0000 - 0x17_ffff_ffff : Off chip DDR memory, uncached

To use this uncached region we create a global DMA memory pool there and
reserve the corresponding area in the cached region.

However the uncached region is fully above the 32bit address limit, so add
a dma-ranges map so the DMA address used for peripherals is still in the
regular cached region below the limit.

Link: https://github.com/starfive-tech/JH7100_Docs/blob/main/JH7100%20Data%20Sheet%20V01.01.04-EN%20(4-21-2021).pdf
Signed-off-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>