ARM: at91/dts: USB host vbus is active low

Change vbus gpio configuration in .dts files to switch to
active low configuration.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: stable <stable@vger.kernel.org>