daemon: add API to get kernel symbols

This is useful because we might not have access to kernel symbols from
user applications which are not root. Various distributions are starting
to censor kernel addresses without root.

This allows the clients to fetch the symbol addresses without having to
be root themselves.

data/org.gnome.Sysprof2.xml

@@ -20,5 +20,20 @@
    <arg name="flags" type="t" direction="in"/>
    <arg name="perf_stream_fd" type="h" direction="out"/>
   </method>
+
+  <!--
+    GetKernelSymbols:
+
+    Loads the name, type, and address of Linux kernel symbols. This is useful
+    if your system does not provide access to /proc/kallsyms to non-root users.
+
+    Returns: an array of (tys) tuples. t is the address, y is the type, and s
+      is the name.
+
+    Since: 3.28
+  -->
+  <method name="GetKernelSymbols">
+   <arg name="symbols" type="a(tys)" direction="out"/>
+  </method>
  </interface>
 </node>