The API is not suitable for subsystems consisting of multiple devices
and requires severe hacks to use it. To mitigate this, this patch
implements allocation and address space management locally by using
helpers provided by DRM framework, like other DRM drivers do, e.g.
Tegra.

This patch should not introduce any functional changes until the driver
is made to attach subdevices into an IOMMU domain with the generic IOMMU
API, which will happen in following patch. Based heavily on GEM
implementation of Tegra DRM driver.
Signed-off-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Shunqian Zheng <zhengsq@rock-chips.com>
Signed-off-by: Mark Yao <mark.yao@rock-chips.com>
Signed-off-by: rjan Eide <orjan.eide@arm.com>