[E09] fix MACHINEOVERRIDES and fw-sysdata branch
This MR:
- fixes the order in which the "rockchip" override is appended to MACHINEOVERRIDES (should appear before SOC family overrides such as "rk3568")
- for e09, sets in u-boot-seco-rk-fw-sysdata the same SRCBRANCH as u-boot-seco-rk, since they share the same source code
Edited by Alessandro Pecugi