drm/amdgpu: Use vm status_lock to protect pt free

Use vm_status_lock to protect all vm_status state transitions to allow
them to happen without a reservation lock in unlocked page table
updates.

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