sh: USB disable process is needed if romImage boot for EcoVec24

when you use romImage on EcoVec24, 1st Linux will enable USB device.
But no-one disable it.
So re-started Linux will get interrupt before USB driver is attached.
This patch disable USB device at first

Signed-off-by: Kuninori Morimoto <morimoto.kuninori@renesas.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>