soc: qcom: pmic_glink: Introduce base PMIC GLINK driver

The PMIC GLINK service runs on one of the co-processors of some modern
Qualcomm platforms and implements USB-C and battery managements. It uses
a message based protocol over GLINK for communication with the OS, hence
the name.

The driver implemented provides the rpmsg device for communication and
uses auxilirary bus to spawn off individual devices in respsective
subsystem. The auxilirary devices are spawned off from a
platform_device, so that the drm_bridge is available early, to allow the
DisplayPort driver to probe even before the remoteproc has spun up.

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