beaglebone: uncomment eMMC override

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
add 'defconfig' file to use as .config

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

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