libutil: Introduce util_sys and util_sys_get_dev_addr()

Many tools need to identify the device address of a given device. So
far, either the tool had its own implementation, or u2s_getbusid() was
used. Though, u2s_getbusid() was mainly designed for and used by the
DASD tools.

Introduce util_sys with a first function util_sys_get_dev_addr() which
provides a more universal way to identify the device address which is
not limited to one particular device type. The device address represents
either a busid (e.g. DASD), slot address (NVMe), H:C:T:L tuple (SCSI),
or other id types associated with a device.

Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

include/lib/util_sys.h

@@ -0,0 +1,17 @@
+/*
+ * @defgroup util_sys_h  util_sys: SysFS interface
+ * @{
+ * @brief Work with SysFS
+ *
+ * Copyright IBM Corp. 2019
+ *
+ * s390-tools is free software; you can redistribute it and/or modify
+ * it under the terms of the MIT license. See LICENSE for details.
+ */
+
+#ifndef LIB_UTIL_SYS_H
+#define LIB_UTIL_SYS_H
+
+int util_sys_get_dev_addr(const char *dev, char *addr);
+
+#endif /** LIB_UTIL_SYS_H @} */