Both ARM itself and Linux for ARM has been standardizing a fair bit recently. But not to the extent to be fully generic, mostly just enough for portable bootable kernels - and after that you still need all the same custom drivers and configurations to make proper use of a SoC, but it's not nothing.
https://linuxgizmos.com/ebbr-spec-to-bring-standardization-to-embedded-linux-boot-process/