virt: Set reset-cbar on CPUs

Set the reset-cbar property on CPUs used by the virt board,
if they have it. This isn't necessary for correct functioning
under Linux (since the A9 isn't a valid CPU for the virt board),
but it is the correct behaviour.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Message-id: 1394462692-8871-5-git-send-email-peter.maydell@linaro.org
