systemd: enable optional PAM support

This commit enables PAM support in systemd if BR2_PACKAGE_LINUX_PAM is
set. Some essential config files are not installed without the
--enable-pam option.

Signed-off-by: James Balean <james@balean.com.au>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/systemd/systemd.mk

@@ -30,7 +30,6 @@ SYSTEMD_CONF_OPTS += \
 	--enable-blkid \
 	--enable-static=no \
 	--disable-manpages \
-	--disable-pam \
 	--disable-ima \
 	--disable-libcryptsetup \
 	--disable-efi \
@@ -108,6 +107,13 @@ else
 SYSTEMD_CONF_OPTS += --disable-lz4
 endif
 
+ifeq ($(BR2_PACKAGE_LINUX_PAM),y)
+SYSTEMD_DEPENDENCIES += linux-pam
+SYSTEMD_CONF_OPTS += --enable-pam
+else
+SYSTEMD_CONF_OPTS += --disable-pam
+endif
+
 ifeq ($(BR2_PACKAGE_XZ),y)
 SYSTEMD_DEPENDENCIES += xz
 SYSTEMD_CONF_OPTS += --enable-xz