usb_stor_BBB_transport: Do not delay when not required

usb_stor_BBB_transport: Do not delay when not required

There is a 5-ms delay in usb_stor_BBB_transport, which occurs every 10 kiB of
data for fragmented fatload usb, i.e. roughly 500 ms of delay per MiB. This adds
up to quite a bit of delay if you're loading a large ramdisk.

The purpose of this delay should be to debounce the 5-V/100-mA USB power up.
This patch skips the delay if the device has already been queried as ready.

Signed-off-by: Jim Shimer <[email protected]>
Rework following the review:
 - Rebase against the latest u-boot-usb master.
 - Replace typedef with #define.
 - Use the existing flags struct field instead of adding a new field.
 - Remove the setter function.
 - Remove the typecasts.
Signed-off-by: Benoît Thébaudeau <[email protected]>
Cc: Marek Vasut <[email protected]>
Cc: Ilya Yanok <[email protected]>
Cc: Stefan Herbrechtsmeier <[email protected]>
Cc: Jim Shimer <[email protected]>