pxe: try bootz if bootm fails to find a valid image

Standard pxelinux servers will typically use a zImage rather than u-boot
image format, so fallback to bootz if bootm fails.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
[tushar.behera@linaro.org: Cherry-picked to current tracking branch]
Signed-off-by: Tushar Behera <tushar.behera@linaro.org>
1 file changed