chore(pm_dfs): Fix missing code block

Add in a code block for a Linux command that is referenced.

Signed-off-by: Kendall Willis <[email protected]>

Author: kwillis01

source/linux/Foundational_Components/Power_Management/pm_dfs.rst

@@ -48,7 +48,8 @@ based on the governors.
 The driver can be built into the kernel as a static module, dynamic
 module, or both.
 
-$ make menuconfig
+.. code-block:: console
+   $ make menuconfig
 
 Select CPU Power Management from the main menu.