[Libomptarget] Disable the 'mapping/prelock.cpp' test on AMDGPU

Summary:
This test was not functional on the new plugins, now that the old ones
have been deleted it doesn't work. Disable until we get a fix.

openmp/libomptarget/test/mapping/prelock.cpp

@@ -1,12 +1,13 @@
 // RUN: %libomptarget-compilexx-generic
-// RUN: env LIBOMPTARGET_NEXTGEN_PLUGINS=0 %libomptarget-run-generic %fcheck-generic
+// RUN: %libomptarget-run-generic %fcheck-generic
 
 // UNSUPPORTED: aarch64-unknown-linux-gnu
 // UNSUPPORTED: aarch64-unknown-linux-gnu-LTO
 // UNSUPPORTED: nvptx64-nvidia-cuda
 // UNSUPPORTED: nvptx64-nvidia-cuda-LTO
 // UNSUPPORTED: x86_64-pc-linux-gnu
 // UNSUPPORTED: x86_64-pc-linux-gnu-LTO
+// UNSUPPORTED: amdgcn-amd-amdhsa
 
 #include <cstdio>