hw/arm/boot: Don't set up ATAGS for autogenerated dtb booting

hw/arm/boot: Don't set up ATAGS for autogenerated dtb booting

The code which decides whether to set up the ATAGS data structure on
reset was using the wrong conditional, which meant we were creating
an ATAGS structure when doing a device-tree boot if the dtb was
autogenerated by the board. This is harmless, but unnecessary, so
bring it in to line with user-provided-dtb boots.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Message-id: 1388326833-656-1-git-send-email-peter.maydell@linaro.org