cdc: INF file fixes

Add a .NT. on DriverInstall sections as it is apparently necessary.

This fixes a problem where Windows was only receiving
every 2nd transaction of input data until some amount of data had been
sent.
usb: Clear endpoint 0 stall manually on PIC16 and PIC18

The datasheets say that endpoint 0 stalls will be cleared automatically by
the hardware when a SETUP packet arrives.  This does not happen on PIC16
and PIC18 MCUs, but does on PIC24 and PIC32.