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: I3faf95eacc653a7f73ad6267be9267c449c61275
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/meson.build b/meson.build
index 828c131..060907c 100644
--- a/meson.build
+++ b/meson.build
@@ -34,7 +34,7 @@
     ],
     dependencies:
     [
-        dependency('systemd'),
+        dependency('libsystemd'),
         dependency('sdbusplus'),
         dependency('ncurses'),
         dependency('threads'),