calao: use zImage on usb-a9263 and usb-a9g20 lpw

The board boot more fast with a zImage than a uImage
as the kernel will not have to be relocated during the decompression.

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>