osmo-bts-trx: Add multiTRX support

Support is limited to 1 osmo-trx with 1 phy and multiple instances.

Change-Id: If2bda5ec7ac9fa3fe6bc5d71f323c3ccc2a70158
diff --git a/example/defaults.conf b/example/defaults.conf
index fc4c324..7ad5e1f 100644
--- a/example/defaults.conf
+++ b/example/defaults.conf
@@ -76,6 +76,9 @@
     - phys_chan_config: TCH/F # nanobts only supports PDCH in TRX0.
     - phys_chan_config: TCH/F
 
+osmo_bts_trx:
+  max_trx: 2
+
 osmo_trx:
   type: uhd
   launch_trx: true