Add support to enable EGPRS

Change-Id: I682f0c1b4cb97b704d646f18f54e748baaefd677
diff --git a/src/osmo_gsm_tester/resource.py b/src/osmo_gsm_tester/resource.py
index 3f2ddc7..6898926 100644
--- a/src/osmo_gsm_tester/resource.py
+++ b/src/osmo_gsm_tester/resource.py
@@ -57,6 +57,7 @@
         'bts[].direct_pcu': schema.BOOL_STR,
         'bts[].ciphers[]': schema.CIPHER,
         'bts[].channel_allocator': schema.CHAN_ALLOCATOR,
+        'bts[].gprs_mode': schema.GPRS_MODE,
         'bts[].num_trx': schema.UINT,
         'bts[].max_trx': schema.UINT,
         'bts[].trx_list[].addr': schema.IPV4,