USB: Sane memory allocation in option driver

The option driver
- violates DMA coherency rules
- allocates ~16500 bytes in one chunk
This patch splits out the buffers and uses __get_free_page() to avoid
higher order allocations.

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Acked-By: Matthias Urlichs <matthias@urlichs.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>