util: move src/basic/creds-util.[ch] → src/shared/

This is preparation for adding encryption support to the credentials
logic, and we thus would like to add more deps. Let's hence move things
from src/basic/ to src/shared, so that we can rely on the OpenSSL
utilities already in src/shared.

src/basic/meson.build

@@ -29,8 +29,6 @@ basic_sources = files('''
         chattr-util.h
         conf-files.c
         conf-files.h
-        creds-util.c
-        creds-util.h
         def.h
         dirent-util.c
         dirent-util.h

src/shared/meson.build

@@ -81,6 +81,8 @@ shared_sources = files('''
         coredump-util.h
         cpu-set-util.c
         cpu-set-util.h
+        creds-util.c
+        creds-util.h
         cryptsetup-util.c
         cryptsetup-util.h
         daemon-util.h