Integrate seco-base/srcrev-from-custom
Commit: https://git.seco.com/edgehog/seco-base/-/commit/11683219b2c55e38be953a8d66cc212739d14e6a
[SRCREV][SETUP-ENVIRONMENT] copy SRCREV.conf from custom layer if present
If there's a custom layer and it contains a conf/SRCREV.conf file, copy that file instead of the one in the machine/architecture layers. Also refactor some code.