Implement hip_ldg Functions into HIP header

Move all the function definitions for hip_ldg.cpp into hip_ldg.h header and enable for HIP clang path.

tests/src/deviceLib/hip_test_ldg.cpp

@@ -35,7 +35,7 @@ THE SOFTWARE.
 #include "hip/hip_vector_types.h"
 #include "test_common.h"
 
-#if (__hcc_workweek__ >= 16164) || defined(__HIP_PLATFORM_NVCC__)
+#if (__hcc_workweek__ >= 16164) || defined(__HIP_PLATFORM_NVCC__) || defined(__HIP_CLANG_ONLY__)
 
 #define HIP_ASSERT(x) (assert((x) == hipSuccess))