extras: add layer

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
extras: gadget-init: import from meta-ti

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
extras: bone101: import from meta-ti

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
extras: bonescript: import from meta-ti

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
extras: beaglebone-getting-started: import from meta-ti

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
README.md: add meta-beagleboard-extras

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