usb_storage: Restore non-EHCI support

The commit 5dd95cf9 made the MSC driver EHCI-specific. This patch restores a
basic support of non-EHCI HCDs, like before that commit.

The fallback transfer size is certainly not optimal, but at least it should work
like before.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Ilya Yanok <ilya.yanok@cogentembedded.com>
Cc: Stefan Herbrechtsmeier <stefan@herbrechtsmeier.net>