Instead of initializing USB as soon as bootcmd is executed, defer it
until the first boot device that (potentially in the case of network)
uses USB is scanned. This avoids initializing USB when booting from MMC,
so speeds that up.
Signed-off-by: NStephen Warren <swarren@nvidia.com>
Signed-off-by: NTom Warren <twarren@nvidia.com>