drm/amdkfd: check if vm ready in svm map and unmap to gpu

drm/amdkfd: check if vm ready in svm map and unmap to gpu

Don't map or unmap svm range to gpu if vm is not ready for updates.

Why: DRM entity may already be killed when the svm worker try to
update gpu vm.

Signed-off-by: YuanShang <YuanShang.Mao@amd.com>
Reviewed-by: Philip Yang <philip.yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 55f8e366c326980174a4f2b9501b524d8eb25135)