meson: switch code dependency to libsystemd

For a while now systemd has packaged a separate `libsystemd`.  For
meson dependency, `systemd` should be used when looking for systemd
service file paths and `libsystemd` should be used for `sd_*` functions.

Update the dependency accordingly.

Change-Id: I2de6ab74c3384339a9f393d3149eabaccf1a5ba4
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/lib/meson.build b/lib/meson.build
index 9c65652..1e2f51f 100644
--- a/lib/meson.build
+++ b/lib/meson.build
@@ -7,9 +7,9 @@
 threads_dep = dependency('threads')
 
 phosphor_logging_deps = [
+    libsystemd_dep,
     pdi_dep,
     sdbusplus_dep,
-    systemd_dep,
     threads_dep
 ]