Documentation: DT: dma: Delete binding doc for AXI DMA

The AXI DMA support is added to the existing AXI VDMA
driver. Device tree binding information also updated
in the VDMA binding doc.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>