Add a command to print a list of available block device drivers,
and for each, the list of known block devices.
Signed-off-by: Niel Fourie <lusus@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Stefan Roese <sr@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Stefan Roese <sr@denx.de>
