enb_amarisoft: add "sdr" as rf_dev_type and rx_ant parameter

this allows to use the Amarisoft PCIe cards with OGT

Change-Id: Ia373a78f59538d6dfca390431f85a7af26c9d914
diff --git a/src/osmo_gsm_tester/obj/enb_amarisoft.py b/src/osmo_gsm_tester/obj/enb_amarisoft.py
index 65c94dd..405ed68 100644
--- a/src/osmo_gsm_tester/obj/enb_amarisoft.py
+++ b/src/osmo_gsm_tester/obj/enb_amarisoft.py
@@ -37,7 +37,7 @@
     schema.register_config_schema('amarisoftenb', config_schema)
 
 def rf_type_valid(rf_type_str):
-    return rf_type_str in ('uhd', 'zmq')
+    return rf_type_str in ('uhd', 'zmq', 'sdr')
 
 class AmarisoftENB(enb.eNodeB):