pinctrl: qcom: ssbi-pmic: promote driver to sub system level

This patch promotes the driver to subsystem level as the pins will be
used by many drivers which come up a the same level. So moving this
driver to subsystem level would make sure that there are not many
deffered probes.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>