dmaengine: k3dma: Delete axi_config

Axi_config controls whether DMA resources can be accessed in non-secure
mode, such as linux kernel. The register should be set by the bootloader
stage and depends on the device.

Thus, this patch removes axi_config from k3dma driver.

Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Vinod Koul <vkoul@kernel.org>
Cc: Tanglei Han <hantanglei@huawei.com>
Cc: Zhuangluan Su <suzhuangluan@hisilicon.com>
Cc: Ryan Grachek <ryan@edited.us>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: dmaengine@vger.kernel.org
Acked-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Li Yu <liyu65@hisilicon.com>
Signed-off-by: Guodong Xu <guodong.xu@linaro.org>
[jstultz: Minor tweaks to commit message]
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>