[d3d11] Lock immediate context when submitting presentation commands

Otherwise, a race condition occurs if a game submits rendering commands
at the same time as presenting the swap chain image. Only works if
multithreaded protection is enabled, but according to MSDN, it is
illegal to use DXGI commands and the immediate context in parallel.

Fixes stability issues in Tales of Vesperia.

src/d3d11/d3d11_context.h

@@ -700,6 +700,10 @@ namespace dxvk {
             VkImageLayout             OldLayout,
             VkImageLayout             NewLayout);
 
+    D3D10DeviceLock LockContext() {
+      return m_multithread.AcquireLock();
+    }
+
   protected:
     
     D3D11Device* const          m_parent;
@@ -917,10 +921,6 @@ namespace dxvk {
       return pShader != nullptr ? pShader->GetCommonShader() : nullptr;
     }
 
-    D3D10DeviceLock LockContext() {
-      return m_multithread.AcquireLock();
-    }
-
     template<typename Cmd>
     void EmitCs(Cmd&& command) {
       m_cmdData = nullptr;

src/d3d11/d3d11_swapchain.cpp

@@ -368,6 +368,8 @@ namespace dxvk {
           D3D11ImmediateContext*  pContext,
     const vk::PresenterSync&      Sync,
           uint32_t                FrameId) {
+    auto lock = pContext->LockContext();
+
     // Present from CS thread so that we don't
     // have to synchronize with it first.
     m_presentStatus.result = VK_NOT_READY;