AstroBWT OpenCL fixes

- Rewrote main BWT kernel to work properly on Navi
- Fixed nonce iterations in OclWorker
- Fixed memory allocation for AstroBWT

src/backend/opencl/OclWorker.cpp

@@ -145,7 +145,7 @@ bool xmrig::OclWorker::selfTest()
 
 size_t xmrig::OclWorker::intensity() const
 {
-    return m_runner ? m_runner->intensity() : 0;
+    return m_runner ? m_runner->roundSize() : 0;
 }