rockchip: Use atf as firmware and move u-boot to loadables in FIT

The FIT generated after the switch to using binman is using different
values for firmware and loadables properties compared to the old script.

With the old script:
 firmware = "atf-1";
 loadables = "u-boot", "atf-2", ...;

After switch to binman:
 firmware = "u-boot";
 loadables = "atf-1", "atf-2", ...;

This change result in SPL jumping directly into U-Boot proper instead of
initializing TF-A.

With this patch the properties change back to:
 firmware = "atf-1";
 loatables = "u-boot", "atf-2", ...;

Fixes: e0c0efff ("rockchip: Support building the all output files in binman")
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Simon Glass <sjg@chromium.org>