[Hardware][TPU] Optionally import for TPU backend (#18269)
Signed-off-by: Siyuan Liu <lsiyuan@google.com>
Signed-off-by: Jade Zheng <zheng.shoujian@outlook.com>
Co-authored-by: Carol Zheng <cazheng@google.com>
Co-authored-by: Jade Zheng <zheng.shoujian@outlook.com>
Co-authored-by: Hongmin Fan <fanhongmin@google.com>
