Build the uImage file using the kernel build system only when
it is really required, which is only in case KEEPUIMAGE == yes.
Otherwise, just build zImage, since the Yocto build system will
handle the uImage generation for us.
Signed-off-by: Marek Vasut <marex@denx.de> Cc: Richard Purdie <richard.purdie@linuxfoundation.org> Cc: Koen Kooi <koen@dominion.thruhere.net> Cc: Paul Eggleton <paul.eggleton@linux.intel.com> Cc: Ross Burton <ross.burton@intel.com> Cc: Bruce Ashfield <bruce.ashfield@windriver.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
