ANDROID: fix build error when use cpu_cgroup_online vh

When register_trace_rvh_cpu_cgroup_online, it would report error:
declaration of 'struct cgroup_subsys_state' will not be visible
outside of this function:
	TP_PROTO(struct cgroup_subsys_state *css),

So add declaration of 'struct cgroup_subsys_state' on the top of vh.

Bug: 289018298
Fixes: 5f657b04 ("ANDROID: subsystem-specific vendor_hooks.c for sched")
Change-Id: I3da0bee61b193ef9d998ebff79ceb91fec12ceff
Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>