soc: qcom: glink: add channel context reference counting

A channel context always has a reference count of at least one if it is
in the channel list for a transport, but as soon as the list lock is
released, then the count can go to zero leading to an access-after-free
scenario.

Add a reference count whenever a channel context is looked up to ensure
that it stays valid for the duration of use.

Change-Id: Ia3a9c3eac13518f247d2e27f869446460f00890d
Signed-off-by: Eric Holmberg <eholmber@codeaurora.org>