docs: workaround markdown parser error in xen-command-line.markdown

Some versions of markdown (specifically the one in Debian Wheezy, currently
used to generate
http://xenbits.xen.org/docs/unstable/misc/xen-command-line.html) seem to be
confused by nested lists in the middle of multi-paragraph parent list entries
as seen in the com1,com2 entry.

The effect is that the "Default" section of all following entries are replace
by some sort of hash or checksum (at least, a string of 32 random seeming hex
digits).

Workaround this issue by making the decriptions of the DPS options a nested
list, moving the existing nested list describing the options for S into a third
level list. This seems to avoid the issue, and is arguably better formatting in
its own right (at least its not a regression IMHO)

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
(cherry picked from commit ae325e94d2)
(cherry picked from commit 3e9054c523)

docs/misc/xen-command-line.markdown

@@ -211,19 +211,14 @@ Both option `com1` and `com2` follow the same format.
 * Optionally, a clock speed measured in hz can be specified.
 * `DPS` represents the number of data bits, the parity, and the number
   of stop bits.
-
-  `D` is an integer between 5 and 8 for the number of data bits.
-
-  `P` is a single character representing the type of parity:
-
-   * `n` No
-   * `o` Odd
-   * `e` Even
-   * `m` Mark
-   * `s` Space
-
-  `S` is an integer 1 or 2 for the number of stop bits.
-
+  * `D` is an integer between 5 and 8 for the number of data bits.
+  * `P` is a single character representing the type of parity:
+      * `n` No
+      * `o` Odd
+      * `e` Even
+      * `m` Mark
+      * `s` Space
+  * `S` is an integer 1 or 2 for the number of stop bits.
 * `<io-base>` is an integer which specifies the IO base port for UART
   registers.
 * `<irq>` is the IRQ number to use, or `0` to use the UART in poll