the */usb_strings.txt files always assumed that the first line is the
manufacturer string, followed by the product string in the second line.
However, the enum strDescNum had it the other way around. Let's fix it
by adjusting the enum to reality.
Fixes: SYS#3591
This way, host code can dynamically detect which interface supports
which functionality.
The related #defines should be moved to a header file that's shared with
the host application code.
Actually, at device level we want to specify 0, so we can select
individual Class/Subclass values at Interface values.
Table 9-8 of the USB2 Specification is quite clear about this.
* we now actually route the EP0 control requests in DFU mode to the
correct handler (weak linker symbols are tricky)
* we now actually call code to read/write data from/to RAM/FLASH
