slimbus: Manage channel slots only if framework manages bandwidth

If slimbus controller overrides bandwidth management, channel slots
should not be managed since controller is expected to do that.
Slimbus controller will go into idle mode due to this change when
channel setup/teardown is done. Make sure controller can transition
states correctly in runtime-pm suspend, and system-suspend case.

Change-Id: Id41aed822e3c98af8c1fe7db3a3527a1206739be
Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>