MAINTAINERS: add missing xtensa patterns

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 1032406..f4a7e45 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -311,6 +311,8 @@
 F: hw/xtensa/
 F: tests/tcg/xtensa/
 F: disas/xtensa.c
+F: include/hw/xtensa/xtensa-isa.h
+F: default-configs/xtensa*.mak
 
 TriCore
 M: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>