DEVELOPERS: add Martin Kepplinger to relevant packages

* tslib: upstream maintainer
* xf86-input-tslib: upstream maintainer
* x11vnc: somewhat interested

Signed-off-by: Martin Kepplinger <martink@posteo.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

DEVELOPERS

@@ -1050,6 +1050,11 @@ F:	package/zic/
 N:	Martin Hicks <mort@bork.org>
 F:	package/cryptsetup/
 
+N:	Martin Kepplinger <martink@posteo.de>
+F:	package/tslib/
+F:	package/x11r7/xdriver_xf86-input-tslib/
+F:	package/x11vnc/
+
 N:	Mathieu Audat <mathieu.audat@savoirfairelinux.com>
 F:	board/technologic/ts4900/
 F:	configs/ts4900_defconfig