[UI] Add simple support for controller usage in UI

- Disabled unnecessary hotkeys thread when it is not used
- Removed problematic xam_exports static initialization
- Moved xam_dialogs_shown_ and xam_nui_dialogs_shown_ to XamState

src/xenia/kernel/xam/xam_private.h

@@ -17,9 +17,6 @@ namespace xe {
 namespace kernel {
 namespace xam {
 
-bool xeXamIsUIActive();
-bool xeXamIsNuiUIActive();
-
 xe::cpu::Export* RegisterExport_xam(xe::cpu::Export* export_entry);
 
 // Registration functions, one per file.