Add a tag for tracing system server.

#define ATRACE_TAG_BIONIC           (1<<16)

#define ATRACE_TAG_POWER            (1<<17)

#define ATRACE_TAG_PACKAGE_MANAGER  (1<<18)

#define ATRACE_TAG_LAST             ATRACE_TAG_PACKAGE_MANAGER

#define ATRACE_TAG_SYSTEM_SERVER    (1<<19)

#define ATRACE_TAG_LAST             ATRACE_TAG_SYSTEM_SERVER

// Reserved for initialization.

#define ATRACE_TAG_NOT_READY        (1LL<<63)