move log/debug codebase to libosmocore

The logging/debugging code is generic enough to move it into libosmocore
while keeping OpenBSC specific definitions in openbsc itself.

This commit uses the logging support present in libosmocore-0.1.2,
you will have to update your library to this version.
diff --git a/openbsc/src/e1_input.c b/openbsc/src/e1_input.c
index c20359c..fba59a7 100644
--- a/openbsc/src/e1_input.c
+++ b/openbsc/src/e1_input.c
@@ -442,7 +442,7 @@
 			return -EINVAL;
 		}
 
-		debug_set_context(BSC_CTX_BTS, link->trx->bts);
+		log_set_context(BSC_CTX_BTS, link->trx->bts);
 		switch (link->type) {
 		case E1INP_SIGN_OML:
 			msg->trx = link->trx;