Started adding native half math library support

1. Removed HIP_EXPERIMENTAL env variable so that device code will be accessed from LLVM IR
2. Removed soft support from headers and moved to hip_fp16.cpp
3. Added LLVM IR + inline asm to hip_ir.ll
4. Added test for fp16
5. Added barriers for hcc 3.5 and hcc 4.0 for half support
a. Which means, hcc 4.0 can parse __fp16 but hcc 3.5 cant
b. HCC 4.0 code is implemented now, hcc 3.5 will be added later

Change-Id: Ic37859b2688ebb02e168bab643d1882bf4727952

hipamd/bin/hipcc

@@ -220,7 +220,7 @@ if($HIP_PLATFORM eq "hcc"){
   }
 }
 
-if(($HIP_PLATFORM eq "hcc") and defined $ENV{HIP_EXPERIMENTAL}){
+if(($HIP_PLATFORM eq "hcc")){
     $EXPORT_LL=" ";
     $ENV{HCC_EXTRA_LIBRARIES}="$HIP_PATH/lib/hip_ir.ll\n";
 }