PowerStack: AP_Periph working #1155

Job	Run time
build (base)	9m 24s
build (clang)	9m 19s
build-gcc-heli	12m 5s
autotest (sitltest-copter-tests1a)	14m 27s
autotest (sitltest-copter-tests1b)	16m 3s
autotest (sitltest-copter-tests1c)	14m 15s
autotest (sitltest-copter-tests1d)	14m 9s
autotest (sitltest-copter-tests1e)	15m 54s
autotest (sitltest-copter-tests2a)	16m 1s
autotest (sitltest-copter-tests2b)	34m 9s
autotest-heli (sitltest-heli)	13m 59s
	2h 49m 45s

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