drm/amdgpu: remove VI hw bug workaround v3

The workaround simply doesn't work because VM mappings
are controlled by userspace not the kernel.

Additional to that this is just a performance problem
which happens if you have holes in your VM mapping.

v2: adjust virtual addr alignment as well.
v3: fix trivial warning

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Monk Liu  <monk.liu@amd.com> (v1)
Reviewed-by: Jammy Zhou <Jammy.Zhou@amd.com> (v2)