power: supply: Introduce Qualcomm PMIC GLINK power supply

The PMIC GLINK service, running on a coprocessor of modern Qualcomm
platforms, deals with battery charging and fuel gauging, as well as
reporting status of AC and wireless power supplies.

As this is just one of the functionalities provided by the PMIC GLINK
service, this power supply driver is implemented as an auxilirary bus
driver, spawned by the main "pmic glink" driver when the PMIC GLINK
service is detected.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>