lc15: make default config usable
lc15: make default config usable

* add trx-calibration path
* change GSM band to 900

Change-Id: I50bc4a4314a8b48e4000de445f4f05795e1a2d8b
Related: SYS#3722

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts