devargs: make parsing variadic

devargs: make parsing variadic

rte_eal_devargs_parse can be used by EAL subsystems, drivers,
applications alike.

Device parameters may be presented with different structure each time;
as a single declaration string or several strings each describing
different parts of the declaration.

To simplify the use of this parsing facility, its parameters are made
variadic.

Signed-off-by: Gaetan Rivet <gaetan.rivet@6wind.com>
Acked-by: Thomas Monjalon <thomas@monjalon.net>