ti_usb_3410_5052: support alternate firmware

The TI USB serial driver supports specifying alternate vendor and
product IDs (since the chips can and are used in devices under other
vendor/product IDs).  However, the alternate IDs were not loaded in the
combined product table.  This patch also adds support for loading
alternate firmware for alternate vendor/product IDs.

Signed-off-by: Chris Adams <cmadams@hiwaay.net>
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>