dmaengine: xilinx_dma: Introduce helper macro for preparing dma address

This patch introduces the xilinx_prep_dma_addr_t macro which prepares
dma_addr_t from hardware buffer descriptor LSB and MSB fields. It will
be used in simple dma 64-bit programming sequence.

Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Reviewed-by: Appana Durga Kedareswara Rao <appana.durga.rao@xilinx.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>