SWDEV-232428 - Push hostcall implementation to the device layer

This change unifies the hostcall implementation for all the backends,
by pushing the common logic to the device layer. This is done by
replacing the use of hsa_signal_t with device::Signal (a light wrapper
around it).

Change-Id: I7b6fca7930b5a0b199da5d85e2e048354cc04e7b

rocclr/device/gpu/gpudevice.hpp

@@ -102,6 +102,11 @@ class NullDevice : public amd::Device {
     return NULL;
   }
 
+  //! Signal object allocation
+  virtual device::Signal* createSignal() const {
+    return nullptr;
+  }
+
   //! Acquire external graphics API object in the host thread
   //! Needed for OpenGL objects on CPU device
 
@@ -415,6 +420,11 @@ class Device : public NullDevice, public CALGSLDevice {
       const device::Memory& parent  //!< Parent device memory object for the view
       ) const;
 
+  //! Signal object allocation
+  virtual device::Signal* createSignal() const {
+    return nullptr;
+  }
+
   //! Create the device program.
   virtual device::Program* createProgram(amd::Program& owner, amd::option::Options* options = NULL);