USB: serial: Updated support for ICOM devices

I found the original patch on the db0fhn repeater wiki (couldn't find the email
of the origial author) I guess it was never commited.
I updated and added some Icom HAM-radio devices to the ftdi driver.
Added extra comments to make clear what devices it are.

Signed-off-by: Pieter Maes <maescool@gmail.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>