usb-storage: make sddr09 a separate module

This patch (as1207) converts usb-storage's sddr09 subdriver into a
separate module.

An unexpected complication arises because of DPCM devices, in which
one LUN uses the sddr09 transport and one uses the standard CB
transport.  Since these devices can be used even when
USB_STORAGE_SDDR09 isn't configured, their entries in unusual_devs.h
require special treatment.  If SDDR09 isn't configured then the
entries remain in unusual_devs.h; if it is then the entries are
present in unusual_sddr09.h instead.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>