cl: check for cl_khr_fp64 (#16246)

tinygrad/device.py

@@ -372,7 +372,7 @@ def is_dtype_supported(dtype:DType, target:Target|None=None) -> bool:
   if dtype == dtypes.float64:
     match target.device:
       case _ if dtypes.long in EMULATED_DTYPES.tolist(dtypes): return False # double can't be bitcast to anything without long support
-      case "CL": return not OSX
+      case "CL": return "cl_khr_fp64" in target.arch
       case "NULL": return target.renderer not in ("IR3", "QCOMCL")
       case "METAL" | "QCOM": return False
   return True