Add USB serial download protocol support to SPL. If the SoC started
in recovery mode the SPL will immediately switch to SDP and wait for
further downloads/commands from the host side.
Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
Reviewed-by: Stefano Babic <sbabic@denx.de>
Reviewed-by: Łukasz Majewski <lukma@denx.de>
