petitboot: Add --verbose option to petitboot when we're configured for debug

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
package/busybox: Add pxepathprefix patch for udhcpc

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
package/petitboot: Update version to b90b84b3

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>