[OpenMP] Print loaded envar when debug flag is enabled (#520)

Print out the loaded envars when `LIBOMPTARGET_DEBUG=1`

example output:
```
TARGET AMDGPU RTL --> Envar config for MI210 is used.
TARGET AMDGPU RTL --> Loaded envar: OMPX_UseMultipleSdmaEngines=1, OMPX_AdjustNumTeamsForXteamRedSmallBlockSize=0
```

---------

Co-authored-by: Ron Lieberman <ron.lieberman@amd.com>

Author: Kewen12

offload/plugins-nextgen/amdgpu/src/rtl.cpp

@@ -3150,6 +3150,16 @@ struct AMDGPUDeviceTy : public GenericDeviceTy, AMDGenericDeviceTy {
       OMPX_XTeamReductionOccupancyBasedOpt =
           EnvarConfig.OMPX_XTeamReductionOccupancyBasedOpt;
     }
+    // Print potential GPU envars.
+    DP("Loaded per GPU envars:\n"
+       "  OMPX_UseMultipleSdmaEngines=%d\n"
+       "  OMPX_AdjustNumTeamsForXteamRedSmallBlockSize=%d\n"
+       "  OMPX_XteamBlockSize=%d\n"
+       "  OMPX_XTeamReductionOccupancyBasedOpt=%d\n",
+       EnvarConfig.OMPX_UseMultipleSdmaEngines,
+       EnvarConfig.OMPX_AdjustNumTeamsForXteamRedSmallBlockSize,
+       EnvarConfig.OMPX_XteamBlockSize,
+       EnvarConfig.OMPX_XTeamReductionOccupancyBasedOpt);
   }
 
   ~AMDGPUDeviceTy() {}