docs/misra: add Rule 7.4 and 9.4

Rule 9.4 is non-controversial and we have no violations.

Rule 7.4 is considered a good idea with the caveat that assigning a
string literal to const void is allowed. I added a note to specify it.

Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>

docs/misra/rules.rst

@@ -203,6 +203,15 @@ maintainers if you want to suggest a change.
      - The lowercase character l shall not be used in a literal suffix
      -
 
+   * - `Rule 7.4 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_07_04.c>`_
+     - Required
+     - A string literal shall not be assigned to an object unless the
+       object type is pointer to const-qualified char
+     - All "character types" are permitted, as long as the string
+       element type and the character type match. (There should be no
+       casts.) Assigning a string literal to any object with type
+       "pointer to const-qualified void" is allowed.
+
    * - `Rule 8.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_08_01.c>`_
      - Required
      - Types shall be explicitly specified
@@ -275,6 +284,11 @@ maintainers if you want to suggest a change.
        braces
      -
 
+   * - `Rule 9.4 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_09_04.c>`_
+     - Required
+     - An element of an object shall not be initialized more than once
+     -
+
    * - `Rule 12.5 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_12_05.c>`_
      - Mandatory
      - The sizeof operator shall not have an operand which is a function