libarchive: Add packageconfig knob for libb2

libarchive: Add packageconfig knob for libb2

automatic detection could result in inconsistent host dependencies
since it will be enabled for libarchive-native if the build host has
libb2 installed and this can then fail on hosts which do not have
this library installed

Fixes errors like
recipe-sysroot-native/usr/bin/opkg: error while loading shared libraries: libb2.so.1: cannot open shared object file: No such file or directory

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>