usb_dev: Double buffer IN packets instead of quad-buffering

Only store two packets of pre-fetched read data, as this is sufficient for
most cases.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
usb_dev: Program data to chip on IN packets

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>