GPU backend

Adds GPU backend and "CUDA" feature to all the tests. As of MR creation, there were no forks in tested IRs so only vanilla non-parallel (single block, single thread) codegen has been tested.

hercules_samples/matmul/src/gpu.sch

@@ -12,4 +12,3 @@ dce(*);
 float-collections(*);
 
 gcm(*);
-xdot[true](*);