Input: iforce - use DMA-safe buffores for USB transfers

USB transport has to use cache line-aligned buffers for transfers to avoid
DMA issues; serio doe snot have such restrictions. Let's move "data_in"
buffer from main driver structure into transport modules and make sure USB
requirements are respected.

Tested-by: Tim Schumacher <timschumi@gmx.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>