drm/kfd: Correct pinned buffer handling at kfd restore and validate process

This reverts commit 8a774fe9 ("drm/amdgpu: avoid restore process run into dead loop")
since buffer got pinned is not related whether it needs mapping
And skip buffer validation at kfd driver if the buffer has been pinned.

Signed-off-by: Xiaogang Chen <Xiaogang.Chen@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>