s390x/css: introduce read-only property type for device ids

Let's introduce a read-only property type that handles device ids of the
CssDevId type used for channel devices for future use. e.g. exposing the
busid of an I/O subchannel that is assigned to a ccw device.
Signed-off-by: NDong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>

hw/s390x/css.c

@@ -1894,6 +1894,13 @@ PropertyInfo css_devid_propinfo = {
     .set = set_css_devid,
 };
 
+PropertyInfo css_devid_ro_propinfo = {
+    .name = "str",
+    .description = "Read-only identifier of an I/O device in the channel "
+                   "subsystem, example: fe.1.23ab",
+    .get = get_css_devid,
+};
+
 SubchDev *css_create_virtual_sch(CssDevId bus_id, Error **errp)
 {
     uint16_t schid = 0;

include/hw/s390x/css.h

@@ -172,6 +172,11 @@ extern PropertyInfo css_devid_propinfo;
 #define DEFINE_PROP_CSS_DEV_ID(_n, _s, _f) \
     DEFINE_PROP(_n, _s, _f, css_devid_propinfo, CssDevId)
 
+extern PropertyInfo css_devid_ro_propinfo;
+
+#define DEFINE_PROP_CSS_DEV_ID_RO(_n, _s, _f) \
+    DEFINE_PROP(_n, _s, _f, css_devid_ro_propinfo, CssDevId)
+
 /**
  * Create a subchannel for the given bus id.
  *