Integrate meta-seco-rk/fix-u-boot-srcbranch
[UBOOT][SRCBRANCH] fix u-boot SRCBRANCH assignment priority
Use lowest priority to assign SRCBRANCH variable in u-boot-seco-rk-common.inc. This way: * u-boot-seco-rk_2017.09 and u-boot-seco-rk_PX30.2017.09 continue pointing to branch seco_2017.09 * u-boot-seco-rk_RK3568.2017.09 and u-boot-seco-rk_RK3588.2017.09 correctly override SRCBRANCH and point to branch seco_2017.09_next. This doesn't change anything for E14 and E35 because in meta-seco-evoca and meta-seco-technogym this variable is assigned to seco_2017.09_next with highest priority. This is useful for E09 since it's going to be merged in seco_2017.09_next, but the RK3568 recipe wrongly points to seco_2017.09 at the moment.