gitadora: (arena model) asio option (#718)

## Link to GitHub Issue or related Pull Request, if one exists
#717 

## Description of change
Add an option to override the ASIO device.

By default the game will try to use any ASIO driver that contains the
string `XONAR` in it.

## Testing
Tested with FlexASIO.

src/spice2x/games/gitadora/asio.h

@@ -0,0 +1,12 @@
+#pragma once
+
+namespace games::gitadora {
+
+    // installs IAT registry hooks in gfdm.dll that redirect the game's
+    // ASIO driver lookup (hard-coded "XONAR" substring) to a user-chosen
+    // driver name read from games::gitadora::ASIO_DRIVER.
+    //
+    // safe to call unconditionally; if ASIO_DRIVER is unset the hooks
+    // forward every call straight through to advapi32.
+    void asio_hook_init();
+}