dmaengine: vdma: Add clock support

Added basic clock support for axi dma's.
The clocks are requested at probe and released at remove.

Reviewed-by: Shubhrajyoti Datta <shubhraj@xilinx.com>
Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>