ANDROID: rwsem: Export rwsem_waiter struct for loadable modules

The rwsem_waiter struct is needed in vendor hook alter_rwsem_list_add.
It has parameter sem which is a struct rw_semaphore (already export in
rwsem.h), inside the structure there is a wait_list to link
"struct rwsem_waiter" items. The task information in each item of the
wait_list is needed to be referenced in vendor loadable modules.

Bug: 174902706
Change-Id: Ic7d21ffdd795eaa203989751d26f8b1f32134d8b
Signed-off-by: Huang Yiwei <hyiwei@codeaurora.org>
Signed-off-by: Vamsi Krishna Lanka <quic_vamslank@quicinc.com>