Add sideload, fastboot as reboot targets in init

Rebooting to these targets requires writing bootloader
messages and thus root. Moving them into init means that
adb, reboot don't need root to use these targets.

Test: try rebooting to these targets
Bug: 78793464
Change-Id: Ia002d1e3b1cb0c0616f60435fb9af4dce162cf84