Revert SWDEV-512344 - Unmap all subbuffers (#26)

This reverts commit 0b69120cfcb5b4689d9f2037b1a01e274d85c20f.

hipamd/src/hip_vm.cpp

@@ -366,6 +366,12 @@ hipError_t hipMemUnmap(void* ptr, size_t size) {
   cmd->enqueue();
   cmd->awaitCompletion();
   cmd->release();
+  vaddr_sub_obj->release();
+
+  // restore the original pa of the generic allocation
+  hip::GenericAllocation* ga
+    = reinterpret_cast<hip::GenericAllocation*>(phys_mem_obj->getUserData().data);
+  ga->release();
 
   HIP_RETURN(hipSuccess);
 }