procps-ng: install binaries in /bin and /sbin

This way the busybox counterparts are overwritten and we will not end up
with procps-ng binaries in /usr/bin and /usr/sbin, and busybox symlinks
for the same tools in /bin and /sbin.

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>