libarchive: make bsdtar and bsdcpio binaries configurable

libarchive comes with two binaries, bsdtar and bsdcpio that used
to be installed by default. This change makes this configurable
with the default not to build and install the binaries.

Signed-off-by: Sven Neumann <s.neumann@raumfeld.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>