Revert "[SYCL] Add generic impl for bf16 fabs" (#8061)

Reverts #7959

See #8040 (comment)

Author: aelovikov-intel

sycl/include/sycl/ext/oneapi/experimental/bfloat16_math.hpp

@@ -52,21 +52,18 @@ std::enable_if_t<std::is_same<T, bfloat16>::value, T> fabs(T x) {
   oneapi::detail::Bfloat16StorageT XBits = oneapi::detail::bfloat16ToBits(x);
   return oneapi::detail::bitsToBfloat16(__clc_fabs(XBits));
 #else
-  if (!isnan(x)) {
-    const static oneapi::detail::Bfloat16StorageT SignMask = 0x8000;
-    oneapi::detail::Bfloat16StorageT XBits = oneapi::detail::bfloat16ToBits(x);
-    x = ((XBits & SignMask) == SignMask)
-            ? oneapi::detail::bitsToBfloat16(XBits & ~SignMask)
-            : x;
-  }
-  return x;
+  std::ignore = x;
+  throw runtime_error(
+      "bfloat16 math functions are not currently supported on the host device.",
+      PI_ERROR_INVALID_DEVICE);
 #endif // defined(__SYCL_DEVICE_ONLY__) && defined(__NVPTX__)
 }
 
 template <size_t N>
 sycl::marray<bfloat16, N> fabs(sycl::marray<bfloat16, N> x) {
-  sycl::marray<bfloat16, N> res;
 #if defined(__SYCL_DEVICE_ONLY__) && defined(__NVPTX__)
+  sycl::marray<bfloat16, N> res;
+
   for (size_t i = 0; i < N / 2; i++) {
     auto partial_res = __clc_fabs(detail::to_uint32_t(x, i * 2));
     std::memcpy(&res[i * 2], &partial_res, sizeof(uint32_t));
@@ -77,12 +74,13 @@ sycl::marray<bfloat16, N> fabs(sycl::marray<bfloat16, N> x) {
         oneapi::detail::bfloat16ToBits(x[N - 1]);
     res[N - 1] = oneapi::detail::bitsToBfloat16(__clc_fabs(XBits));
   }
+  return res;
 #else
-  for (size_t i = 0; i < N; i++) {
-    res[i] = fabs(x[i]);
-  }
+  std::ignore = x;
+  throw runtime_error(
+      "bfloat16 math functions are not currently supported on the host device.",
+      PI_ERROR_INVALID_DEVICE);
 #endif // defined(__SYCL_DEVICE_ONLY__) && defined(__NVPTX__)
-  return res;
 }
 
 template <typename T>