efi_loader: Add an EFI_CALL() macro

Rather than open-coding EFI_EXIT() + callback + EFI_ENTRY(), introduce
an EFI_CALL() macro.  This makes callbacks into UEFI world (of which
there will be more in the future) more concise and easier to locate in
the code.

Signed-off-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c
index 17c531a..849d229 100644
--- a/lib/efi_loader/efi_boottime.c
+++ b/lib/efi_loader/efi_boottime.c
@@ -120,9 +120,7 @@
 		return;
 	event->signaled = 1;
 	if (event->type & EVT_NOTIFY_SIGNAL) {
-		EFI_EXIT(EFI_SUCCESS);
-		event->notify_function(event, event->notify_context);
-		EFI_ENTRY("returning from notification function");
+		EFI_CALL(event->notify_function(event, event->notify_context));
 	}
 }