USB: overhaul of mos7840 driver

This fixes:

- breaking DMA rules about buffers
- usage of _global_ variables to save a single device's attributes
- racy access to urb->status
- smp monotonity issue with statistics
- use of one buffer for many simultaneous URBs
- error handling introduced
- several instances of following NULL pointers
- use after free
- unnecessary GFP_ATOMIC
- GFP_KERNEL in interrupt
- various cleanups
- write room granularity issue that bit cdc-acm
- race in shutdown

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>