docs/misra: add R17.2 and R18.2

The Xen community is already informally following both rules. Let's make
it explicit. Both rules have zero violations, only cautions. While we
want to go down to zero cautions in time, adding both rules to rules.rst
enables us to immediately make both rules gating in the ECLAIR job part
of gitlab-ci.

Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com>
Acked-by: Bertrand Marquis <bertrand.marquis@arm.com>

docs/misra/rules.rst

@@ -561,6 +561,13 @@ maintainers if you want to suggest a change.
      - The features of <stdarg.h> shall not be used
      -
 
+   * - `Rule 17.2 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_17_02.c>`_
+     - Required
+     - Functions shall not call themselves, either directly or indirectly
+     - Limited forms of recursion are allowed if the recursion is bound
+       (there is an upper limit and the upper limit is enforced.) The
+       bounding should be explained in a comment or in a deviation.
+
    * - `Rule 17.3 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_17_03.c>`_
      - Mandatory
      - A function shall not be declared implicitly
@@ -593,6 +600,12 @@ maintainers if you want to suggest a change.
        submitting new patches please try to decrease the number of
        violations when possible.
 
+   * - `Rule 18.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_18_01.c>`_
+     - Required
+     - A pointer resulting from arithmetic on a pointer operand shall
+       address an element of the same array as that pointer operand
+     -
+
    * - `Rule 18.2 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_18_02.c>`_
      - Required
      - Subtraction between pointers shall only be applied to pointers