kernel-doc/rst: add support for struct/union/enum member references

Link "&foo->bar", "&foo->bar()", "&foo.bar", and "&foo.bar()" to the
struct/union/enum foo definition. The members themselves do not
currently have anchors to link to, but this is better than nothing, and
promotes a universal notation.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>