Change back the TPL of PCD from TPL_CALLBACK to TPL_NOTIFY because the following...

Change back the TPL of PCD from TPL_CALLBACK to TPL_NOTIFY because the following issue is found:
When we manually connect a device path mapping to the serial terminal with non-default band rate, the SerialIo driver would Reinstall its device path protocol eventually causing ConSplitter::DriverBindingStart() to run and finally would call PcdGet32 (PcdConOutColumn) in ConsplitterSetConsoleOutMode().
Since SerialIo driver raises TPL to TPL_NOTIFY initially, the call to PcdGet32 would cause TPL assertion if TPL of PCD is TPL_CALLBACK.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@10188 6f19259b-4bc3-4df7-8a09-765794883524