doc: Set correct syntax highlighting style

Several code blocks do not specify a language for syntax
highlighting. This results in Sphinx using a default highlighter
which is Python.

This patch adds the correct language to each code block that doesn't
already specify it.

Change-Id: Icce1949aabfdc11a334a42d49edf55fa673cddc3
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
diff --git a/docs/design/firmware-design.rst b/docs/design/firmware-design.rst
index 27d0948..e9384e6 100644
--- a/docs/design/firmware-design.rst
+++ b/docs/design/firmware-design.rst
@@ -2304,7 +2304,7 @@
 Subscribed handlers must be of type ``pubsub_cb_t``, with following function
 signature:
 
-::
+.. code:: c
 
    typedef void* (*pubsub_cb_t)(const void *arg);
 
@@ -2331,7 +2331,7 @@
 
 -  Define the event ``foo`` in the ``pubsub_events.h``.
 
-   ::
+   .. code:: c
 
       REGISTER_PUBSUB_EVENT(foo);
 
@@ -2467,7 +2467,7 @@
 From outside TF-A, timestamps for individual CPUs can be retrieved by calling
 into ``pmf_smc_handler()``.
 
-.. code:: c
+::
 
     Interface : pmf_smc_handler()
     Argument  : unsigned int smc_fid, u_register_t x1,
@@ -2597,7 +2597,7 @@
 directive by defining ``MARCH32_DIRECTIVE``.
 I.e:
 
-::
+.. code:: make
 
    MARCH32_DIRECTIVE := -mach=armv7-a