drm/rockchip: Detach from ARM DMA domain in attach_device

Since commit 1ea2a07a ("iommu: Add DMA ownership management
interfaces") the Rockchip display driver on the Firefly RK3288 fails to
initialise properly. This is because ARM DMA domain is still attached.

Let's follow the lead of exynos and tegra and add code to explicitly
remove the ARM domain before attaching a new one.

Suggested-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>