drm/rockchip: Use common IOMMU API to attach devices

Rockchip DRM used the arm special API, arm_iommu_*(), to attach
iommu for ARM32 SoCs. This patch convert to common iommu API
so it would support ARM64 like RK3399.

Since previous patch added support for direct IOMMU address space
management, there is no need to use DMA API anymore and this patch wires
things to use the new method.

Signed-off-by: Shunqian Zheng <zhengsq@rock-chips.com>
Signed-off-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Mark Yao <mark.yao@rock-chips.com>