DEVELOPERS: add entry for the bananapi_m2_ultra_defconfig

Lothar contributed this board not long ago, so let's assume he is
willing to take care of it.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

DEVELOPERS

@@ -1233,6 +1233,8 @@ N:	Lionel Orry <lionel.orry@gmail.com>
 F:	package/mongrel2/
 
 N:	Lothar Felten <lothar.felten@gmail.com>
+F:	board/bananapi/bananapi-m2-ultra/
+F:	configs/bananapi_m2_ultra_defconfig
 F:	package/ti-sgx-demos/
 F:	package/ti-sgx-km/
 F:	package/ti-sgx-um/