kdoc: xforms_lists: handle DECLARE_PER_CPU() in kernel-doc

kdoc: xforms_lists: handle DECLARE_PER_CPU() in kernel-doc

Add support for DECLARE_PER_CPU() as a var (variable) as used in
<linux/netfilter/x_tables.h>.

Warning: include/linux/netfilter/x_tables.h:345 function parameter 'seqcount_t' not described in 'DECLARE_PER_CPU'
Warning: include/linux/netfilter/x_tables.h:345 function parameter 'xt_recseq' not described in 'DECLARE_PER_CPU'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20260614052452.1557987-1-rdunlap@infradead.org>