Add fastbootd.

Fastbootd is started by recovery, and communicates
over usb with the fastboot protocol.

Add additional fastboot commands to move in and out of
fastbootd. "fastboot reboot recovery" and "fastboot reboot fastboot"

Bug: 78793464
Test: fastboot reboot recovery, fastboot reboot fastboot
Change-Id: Iffb77b2d3ceefb7335c38aa9fba7bd17821484f0