drm/radeon: add userptr flag to register MMU notifier v3

Whenever userspace mapping related to our userptr change
we wait for it to become idle and unmap it from GTT.

v2: rebased, fix mutex unlock in error path
v3: improve commit message

Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --cc drivers/gpu/drm/Kconfig
Simple merge

diff --cc drivers/gpu/drm/radeon/Makefile
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon.h
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_device.c
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_gem.c
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_mn.c
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_object.c
Simple merge

diff --cc include/uapi/drm/radeon_drm.h
Simple merge