doc: add CSS support for hlist directive

Lists that are long and narrow can be displayed better using the
hlist directive:

.. hlist::
   :columns: 3

   * item 1
   * item 2
   * item 3
   * item 4
   * item 5
   * item 6
   * item 7
   * item 8
   * item 9
   * item 10

Will display as:

   * item 1  * item 5  * item 8
   * item 2  * item 6  * item 9
   * item 3  * item 7  * item 10
   * item 4

and with this patch, the generated table will display full page width
instead of compact.

Change-Id: I238a22461c45b51911d2d3039c9e5eb0c4dbf23c
Signed-off-by: David B. Kinder <david.b.kinder@intel.com>