soc: qcom: Introduce QMI helpers

Drivers that needs to communicate with a remote QMI service all has to
perform the operations of discovering the service, encoding and decoding
the messages and operate the socket. This introduces an abstraction for
these common operations, reducing most of the duplication in such cases.

Change-Id: I937a35d631280843c0d9e13a7a4e103c35b3905b
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Patch-mainline: linux-arm-msm @ 15/11/2017 12:10
[clew@codeaurora.org: Bring downstream up to date by merging differences
 between v1 and v3 patchsets from "soc: qcom: Introduce QMI helpers"]
Signed-off-by: Chris Lew <clew@codeaurora.org>