layerman: activate meta-beagleboard

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
layerman: add meta-minnow BSP

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>

Conflicts:
	sources/layers.txt
README: add Yocto bits

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>