drm/amdgpu: add tmz feature parameter (v2)

This patch adds tmz parameter to enable/disable
the feature in the amdgpu kernel module. Nomally,
by default, it should be auto (rely on the
hardware capability).

But right now, it need to set "off" to avoid
breaking other developers' work because it's not
totally completed.

Will set "auto" till the feature is stable and
completely verified.

v2: add "auto" option for future use.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>