isaspec: Add support for function and entrypoint labels

Functions (i.e. labels reached from call instructions) should be printed
differently from normal labels. In addition we also need to add support
for entrypoints with user-defined names in order to show packet names in
afuc.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23949>

docs/drivers/freedreno/isaspec.rst

@@ -276,6 +276,30 @@ This would produce a disassembly like ``jump #l42`` if the destination is 42
 instructions after the start of the disassembly. The destination would be
 preceded by a line with just ``l42:``.
 
+``branch`` and ``absbranch`` fields can additionally have a ``call="true"``
+attribute. For now, this just changes the disassembly. In particular the label
+prefix is changed to ``fxn`` and an extra empty line before the destination is
+added to visually seperate the disassembly into functions. So, for example, a
+call instruction defined like this:
+
+.. code-block:: xml
+
+   <bitset name="call" extends="#instruction">
+      <display>
+         call #{OFFSET}
+      </display>
+      <pattern low="26" high="31">110010</pattern> <!-- opcode goes here -->
+      <field name="OFFSET" low="0" high="25" type="branch" call="true"/>
+   </bitset>
+
+will disassemble to ``call #fxn42``.
+
+Finally, users with special knowledge about where execution may start can define
+"entrypoints" when disassembling which are printed like function call
+destinations, with an extra empty line, but with an arbitrary user-defined
+name. Names that are ``fxn`` or ``l`` followed by a number are discouraged
+because they may clash with automatically-generated names.
+
 Encoding
 --------