soc: qcom: smd: Refactor channel open and close handling

Refactor opening and closing of channels into two separate functions
instead of open coding this in the various places.

Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>