USB: serial: add symbol serial driver

This is for the Symbol 6608 barcode scanner in a fake "HID" mode.

Thanks to Dalibor Grgec for working with me to get this to start to work
properly.

Cc: Dalibor Grgec <dalibor.grgec@zemris.fer.hr>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>