google-sargo: replace hexagonrpcd config in firmware openrc subpackage
In !5688 (merged), a Pixel 3a subpackage for OpenRC configuration dependent on non-free firmware was added. This includes the HexagonRPCD configuration, but the new subpackage isn't marked as replacing the original configuration from hexagonrpcd-openrc
. Move the replaces=
declaration to the new subpackage.