feat: add cpu/cuda config for prompt guard

Previously prompt guard was hard coded to require cuda which
prevented it from being used on an instance without a cuda
support.

This PR allows prompt guard to be configured to use either cpu
or cuda.

Signed-off-by: Michael Dawson <mdawson@devrus.com>

llama_stack/providers/inline/safety/prompt_guard/config.py

@@ -15,8 +15,14 @@ class PromptGuardType(Enum):
     jailbreak = "jailbreak"
 
 
+class PromptGuardExecutionType(Enum):
+    cpu = "cpu"
+    cuda = "cuda"
+
+
 class PromptGuardConfig(BaseModel):
     guard_type: str = PromptGuardType.injection.value
+    guard_execution_type: str = PromptGuardExecutionType.cuda.value
 
     @classmethod
     @field_validator("guard_type")
@@ -25,8 +31,16 @@ class PromptGuardConfig(BaseModel):
             raise ValueError(f"Unknown prompt guard type: {v}")
         return v
 
+    @classmethod
+    @field_validator("guard_execution_type")
+    def validate_guard_execution_type(cls, v):
+        if v not in [t.value for t in PromptGuardExecutionType]:
+            raise ValueError(f"Unknown prompt guard execution type: {v}")
+        return v
+
     @classmethod
     def sample_run_config(cls, __distro_dir__: str, **kwargs: Any) -> dict[str, Any]:
         return {
             "guard_type": "injection",
+            "guard_execution_type": "cuda",
         }

llama_stack/providers/inline/safety/prompt_guard/prompt_guard.py

@@ -75,7 +75,7 @@ class PromptGuardShield:
         self.temperature = temperature
         self.threshold = threshold
 
-        self.device = "cuda"
+        self.device = self.config.guard_execution_type
 
         # load model and tokenizer
         self.tokenizer = AutoTokenizer.from_pretrained(model_dir)