fastboot: use getopt_long

Modify the fastboot argument parsing to use getopt_long.  This
simplifies argument parsing, and permutes all the commands to the end of
argv to allow parsing them later.

Also moves usb initailization between argument and command processing,
to allow commands to query parameters over usb.

Change-Id: I883572f52c4190c80ee3b4aa4511ea2061a6b734