libpam: set pam module path to ${base_libdir}/security

libpam: set pam module path to ${base_libdir}/security

After upgrading to 1.7.0, the pam module path is set to
${libdir}/security[1]. But from the pam.conf(5) man page, the default
location seems to be "Module location: /lib/security/ or
/lib64/security/, depending on the architecture"[2].

Many third-party pam modules still use {base_libdir}/security as the
default module path, such as pam_lastlog2 (from util-linux), pam_cgroup
(from libcgroup), pam_cap (from libcap), etc.
So currently if you don't use the absolute path to these modules in the
files in /etc/pam.d/, they will not be found:

PAM unable to dlopen(/usr/lib/security/pam_lastlog2.so):
/usr/lib/security/pam_lastlog2.so: cannot open shared object file: No such file or directory

This change only affects sysvinit without usrmerge feature enabled, and
has no effect on systems using systemd.

[1] https://git.openembedded.org/openembedded-core/commit/?id=00eb730291f9630eb70480d37ed48fbadecc547a
[2] https://www.man7.org/linux/man-pages/man5/pam.conf.5.html

Signed-off-by: Yi Zhao <yi.zhao@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>