kirkwood: move usb support to modules

kirkwood: move usb support to modules

USB support built in kernel isn't required for booting.
This patch move USB support to modules.

CONFIG_USB_STORAGE is removed because it can be found in kmod-usb-storage
and all usb support for this targed is moved to kmods.

Tested-by: Cezary Jackiewicz <cezary@eko.one.pl> [nsa310]
Tested-by: Alberto Bursi <bobafetthotmail@gmail.com> [nsa325, ea4500]
Reviewed-by: Sungbo Eo <mans0n@gorani.run>
Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>
[keep CONFIG_SCSI]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>