avr32: take maintainership for atstk1002

I have this board at work, so I can trun tests on it.

Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>

board/atmel/atstk1000/MAINTAINERS

@@ -1,6 +1,6 @@
 ATSTK1000 BOARD
-#M:	Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
-S:	Orphan (since 2014-06)
+M:	Andreas Bießmann <andreas.biessmann@corscience.de>
+S:	Maintained
 F:	board/atmel/atstk1000/
 F:	include/configs/atstk1002.h
 F:	configs/atstk1002_defconfig