[Bug] Add TPU backend option (#32438)

Signed-off-by: Xiongfei Wei <isaacwxf23@gmail.com>

vllm/model_executor/layers/fused_moe/oracle/unquantized.py

@@ -32,6 +32,7 @@ class UnquantizedMoeBackend(Enum):
     TRITON = "TRITON"
     CPU = "CPU"
     XPU = "XPU"
+    TPU = "TPU"
 
 
 # NOTE(zyongye): Unsupported backend means backend
@@ -40,6 +41,7 @@ class UnquantizedMoeBackend(Enum):
 UNSUPPORTED_BACKEND = [
     UnquantizedMoeBackend.CPU,
     UnquantizedMoeBackend.XPU,
+    UnquantizedMoeBackend.TPU,
 ]
 
 
@@ -91,6 +93,8 @@ def select_unquantized_moe_backend(
         backend = UnquantizedMoeBackend.XPU
     if current_platform.is_cpu():
         backend = UnquantizedMoeBackend.CPU
+    if current_platform.is_tpu():
+        backend = UnquantizedMoeBackend.TPU
 
     logger.info_once(_make_log_backend(backend), scope="local")
     return backend