ANDROID: sched: Export sched_domains_mutex for lockdep

If CONFIG_LOCKDEP is enabled, export `sched_domains_mutex` as it is
indirectly accessed by the macro `for_each_domain()`. This allows
vendors to call the `for_each_domain()` macro with CONFIG_LOCKDEP
enabled via the GKI_BUILD_CONFIG_FRAGMENT.

Bug: 176254015
Bug: 301555353
Signed-off-by: Daniel Mentz <danielmentz@google.com>
Change-Id: Ia9f2989de41b2224c63855f2fd129cbeeac4f195
Signed-off-by: Will McVicker <willmcvicker@google.com>
(cherry picked from commit 7171a5de)
(cherry picked from commit e2cdae06)
(cherry picked from commit f6707f35)