dma: xlnx-zynq-devcfg: Fix up XLNX_ZYNQ_DEVCFG_R_MAX

Whilst according to the Zynq TRM this device covers a register region of
0x000 - 0x120. The register region is also shared with XADCIF prefix
registers at 0x100 and above. Due to how the devcfg and the xadc devices
are implemented in QEMU these are separate models with individual mmio
regions. As such the region registered by the devcfg overlaps with the
xadc when initialized in a machine model (e.g. xilinx-zynq-a9).

This patch fixes up the incorrect region size, where
XLNX_ZYNQ_DEVCFG_R_MAX is missing its '/ 4' causing it to be 0x460 in
size. As well as setting the region size to the 0x0 - 0x100 region so
that an xadc device instance can be registered in the correct region to
pair with the devcfg device instance.

Mapping with XLNX_ZYNQ_DEVCFG_R_MAX = 0x118:
  dev: xlnx.ps7-dev-cfg, id ""
    mmio 00000000f8007000/0000000000000460
  dev: xlnx,zynq-xadc, id ""
    mmio 00000000f8007100/0000000000000020

Mapping with XLNX_ZYNQ_DEVCFG_R_MAX = 0x100 / 4:
  dev: xlnx.ps7-dev-cfg, id ""
    mmio 00000000f8007000/0000000000000100
  dev: xlnx,zynq-xadc, id ""
    mmio 00000000f8007100/0000000000000020

Signed-off-by: Nathan Rossi <nathan@nathanrossi.com>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Message-id: 20160921180911.32289-1-nathan@nathanrossi.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
