usb: Rename SPL_USB_SUPPORT to SPL_USB_STORAGE

usb: Rename SPL_USB_SUPPORT to SPL_USB_STORAGE

Since there is the SPL_USB_HOST_SUPPORT for enabling USB support in SPL,
makes more sense to rename the SPL_USB_SUPPORT as SPL_USB_STORAGE.
Everything that is not part of the usb storage support in SPL is now
build under SPL_USB_HOST_SUPPORT.

Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Lukasz Majewski <lukma@denx.de>