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 <[email protected]> [nsa310]
Tested-by: Alberto Bursi <[email protected]> [nsa325, ea4500]
Reviewed-by: Sungbo Eo <[email protected]>
Signed-off-by: Pawel Dembicki <[email protected]>
[keep CONFIG_SCSI]
Signed-off-by: Adrian Schmutzler <[email protected]>