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.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Iae441b2f5607c2247c66632c942d1e75162f0120
diff --git a/meson.build b/meson.build
index 2332607..a3a1216 100644
--- a/meson.build
+++ b/meson.build
@@ -13,7 +13,7 @@
 
 deps = [
   dependency('sdbusplus'),
-  dependency('systemd'),
+  dependency('libsystemd'),
   dependency('boost'),
 ]