tracef.3.txt/tracelog.3.txt: always take variadic variants into account

tracef.3.txt/tracelog.3.txt: always take variadic variants into account

This patch makes the `tracef.3.txt` and `tracelog.3.txt` manual page
sources always mention the variadic variant where the non-variadic
variant is mentioned for consistency.

This patch also changes the `va_list` type from the "SYNOPSIS" sections
as vtracef() and vtracelog() are macros. The type of the `ap` parameter
(`va_list`) is given in the "DESCRIPTION" sections.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I84a795d16a39a483c43f1963189cd7e1faa5c329