dts: arm: xilinx: zynqmp: remove sram0 declaration at SoC level

Remove the universal, unconditional declaration of the RAM area
at the SoC level, due to:

- the hardcoded base address 0 overlapping the exception vectors,
  the ATCM and the BTCM areas.
- the availability of the BTCM not being guaranteed unconditionally
  (config pin dependant)
- the possibility of having a 'black hole' between the ATCM and
  the BTCM depending on the operating mode of the R-cores cluster,
  which leads to a part of the text section being unavailable
- qemu not properly implementing the configuration-dependant
  behaviour of the ATCM and BTCM areas.

Signed-off-by: Immo Birnbaum <mail@birnbaum.immo>