doc: fix uses of back quotes in documentation

ReST defines interpreted text roles where text enclosed by single quotes
can be "intrepreted", for example :ref:`some name` becomes a link to
a label anywhere in the doc set named "some name", :c:func:`funcname()`
becomes a link to the API documentation for "funcname", and
:option:`CONFIG_NAME` becomes a link to, in our case, the documentation
for the generated Kconfig option.

This patch fixes uses of `some name` (without a role) by either adding
an explicit role, or changing to ``some name``, which indicates inline
code block formatting (most likely what was intended).

This is a precursor to changing the default behavior of interpreted
text to treat `some name` as :any:`some name` (as configured in
doc/conf.py), which would attempt to create a link to any available
definition of "some name".

We may not change this default role behavior, but it becomes an option
after the fixes in this patch.  In any case, this patch fixes incorrect
uses of single-quoted text (possibly introduced because GitHub's
markdown language uses single-quoted text for inline code formatting).

Jira: ZEP-2414

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