OcAfterBootCompatLib: Create events with TPL_CALLBACK priority

Logging may save to file, and file services must be invoked with TPL
lower or equal to TPL_CALLBACK. Failing to do so causes OVMF crash.

closes acidanthera/bugtracker#831

Changelog.md

@@ -9,7 +9,7 @@ OpenCore Changelog
 - Fixed rendering macOS installer icons in OpenCanopy
 - Added APFS support with Fusion Drive and enhanced security
 - Added AppleEvent mouse support in OpenCanopy
-- Fixed AppleEvent compatibility with Timer TPL restrictions
+- Fixed AppleEvent and OpenCanopy compatibility with OVMF TPL restrictions
 - Added mouse drivers to the package as OVMF needs one
 
 #### v0.5.7

Library/OcAfterBootCompatLib/ServiceOverrides.c

@@ -1040,7 +1040,7 @@ InstallServiceOverrides (
 
   Status = gBS->CreateEvent (
     EVT_NOTIFY_SIGNAL,
-    TPL_NOTIFY,
+    TPL_CALLBACK,
     SetGetVariableHookHandler,
     BootCompat,
     &BootCompat->ServiceState.GetVariableEvent