dmaengine: xilinx: dpdma: Add missing dependencies to Kconfig

The driver depends on both OF and IOMEM support, express those
dependencies in Kconfig. This fixes a build failure on S390 reported by
the 0day bot.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Jianqiang Chen <jianqiang.chen@xilinx.com>
Reviewed-by: Jianqiang Chen <jianqiang.chen@xilinx.com>
Link: https://lore.kernel.org/r/20210520152420.23986-2-laurent.pinchart@ideasonboard.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>