pmOS support

[samcday]

This needs:

• gibblox: add GptBlockReader #6
• ext4 #7
• Solidify recovery semantics smoo#1
• usb-moded support smoo#16
• gibblox: Android sparse image support #25

[samcday]

Most pmOS downstream kernels will lack necessary ublk enablement. I think many/most are missing EroFS+LZ4 support.

Main blocker is ensuring we can get smoo-gadget handover properly threaded through usb-moded. As it currently stands, once pmOS' userspace has booted far enough, usb-moded would take over ConfigFS and break the smoo link. smoo-gadget daemon itself still needs some work to ensure the SIGHUP handover process actually works ;)