MEDIUM: Refactor init_check and move to checks.c

Refactor init_check so that an error string is returned
rather than alerts being printed by it. Also
init_check to checks.c and provide a prototype to allow
it to be used from multiple C files.

Signed-off-by: Simon Horman <horms@verge.net.au>
diff --git a/include/proto/checks.h b/include/proto/checks.h
index f3d4fa6..1e65652 100644
--- a/include/proto/checks.h
+++ b/include/proto/checks.h
@@ -44,6 +44,8 @@
 	return __health_adjust(s, status);
 }
 
+const char *init_check(struct check *check, int type);
+
 #endif /* _PROTO_CHECKS_H */
 
 /*