drm/amdgpu: track evicted page tables v2

Instead of validating all page tables when one was evicted,
track which one needs a validation.

v2: simplify amdgpu_vm_ready as well

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com> (v1)
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>