soc: qcom: Add socinfo driver

The Qualcomm socinfo driver exposes information about the SoC, its
version and its serial number to user space.

Signed-off-by: Imran Khan <kimran@codeaurora.org>
[Bjorn: Extract code to platform_driver, split patch in multiple]
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
[Vaishali: Simplify declarations, introduce qcom_socinfo struct, Fix
           memory leak, Remove extra code and Misc code refactoring]
Signed-off-by: Vaishali Thakkar <vaishali.thakkar@linaro.org>