MAINTAINERS: add tools/efivar.py to EFI PAYLOAD

tools/efivar.py allows to prepare a file with UEFI variables to preseed
the UEFI variable store.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/MAINTAINERS b/MAINTAINERS
index 8675965..f18a296 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -697,6 +697,7 @@
 F:	cmd/bootefi.c
 F:	cmd/efidebug.c
 F:	cmd/nvedit_efi.c
+F:	tools/efivar.py
 F:	tools/file2include.c
 
 EFI VARIABLES VIA OP-TEE