This way we can model a flexible mapping between any number of PHYs, each having multiple instances, and then map BTSs with TRXx on top of those PHYs.
This removes a lot of copy+paste duplication between different BTS models.
This adds support for a new PHY to OsmoBTS, the Octasic OCTSDR-2G PHY. This is a proprietary GSM PHY running on a familty of Octasic DSPs.