drivers: qcom: rpmh: Setup waitq for passhthru active requests only

Sleep and Wake requests using passthru RPMH API are asynchronous and
hence do not wait. Setup the waitq objects only for active requests
only.

Change-Id: I75991655121ab0849dee9bd10234ecf0239aa803
Signed-off-by: Lina Iyer <ilina@codeaurora.org>