core: keep track of all PIN retry counts

Added a PinRetryCounts property on org.freedesktop.ModemManager.Modem.
This is dictionary that records the number of PIN tries remaining
for each of the possible PIN code types for which the modem is
capable of reporting the count. Also, these counts are kept up
to date across ChangePin and EnablePin operations, not just when
an unlock is attempted.

introspection/org.freedesktop.ModemManager.Modem.xml

@@ -171,8 +171,21 @@
 
     <property name="UnlockRetries" type="u" access="read">
       <tp:docstring>
-        The number of unlock retries remaining for the unlock code given by the property UnlockRequired, or 999 if
-        the device does not support reporting unlock retries.
+        The number of unlock retries remaining for the unlock code given by the
+        property UnlockRequired, or 999 if the device does not support reporting
+        unlock retries. If UnlockRequired is blank, the value of this property
+        is not meaningful.
+      </tp:docstring>
+    </property>
+
+    <property name="PinRetryCounts" type="a{su}" access="read">
+      <tp:docstring>
+        A dictionary in which the keys are the names of the unlock codes
+        specified for the UnlockRequiredProperty, and the values are integers
+        giving the number of PIN tries remaining before the code becomes
+        blocked (requiring a PUK) or permanently blocked. Dictionary entries
+        exist only for the codes for which the modem is able to report retry
+        counts.
       </tp:docstring>
     </property>