efi_loader: notification with TPL_APPLICATION not allowed

The UEFI specification requires event notification levels to be
> TPL_APPLICATION and <= TPL_HIGH_LEVEL.

With the patch the CreateEvent() and CreatedEventEx() services are changed
to check that the notification level is not TPL_APPLICATION.

Reference:
UEFI Specification 2.8 Errata B, table 27 "TPL Restrictions",
"Event Notification Levels"

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>