msm: smd_pkt: Allow multiple users of an SMD_PKT device

Add the usage reference count for every SMD_PKT device. Update the
sequence of operations in device open & close calls. This will enable
multiple user-space users of a SMD_PKT device.

Change-Id: Ic11d0c2e6908f1d82f7aef6a99a0239a92358814
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>