orinoco: cache downloadable firmware image in memory for use during resume

If card is using downloadable firmware (like Agere 9.x), firmware has
to be reloaded during resume. It is not possible to use request_firmware
for that, because tasks are still frozen, so request_firmware will
just timeout and fail. So cache firmware image in memory for later
reuse in ->resume method.

Signed-off-by: Andrey Borzenkov <arvidjaar@mail.ru>
Signed-off-by: John W. Linville <linville@tuxdriver.com>