drm/amdgpu/gmc10: use common invalidation engine helper

Rather than open coding it.  This also changes the free masks
to better reflect the usage by other components.

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