util-linux will check for the exisitance of pam header files and change what is
built, so only build libpam when pam is enabled for DISTRO_FEATURES
(From OE-Core rev: 7e768395622578b3bf944a91a1ac31022c11e245)
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>