pinctrl: qcom: spmi-gpio: add support to enable/disable output

Currently, if the GPIO is configured as output in the bootloader
and user changes the mode to input in HLOS, it would end up
getting configured as input/output. Functionally, this is fine;
however, there may be some requirements where the output needs
to be disabled so that it can be used only for input.

Add support to enable/disable output mode through "output-enable"
or "output-disable" pinctrl properties.

Change-Id: Ie857f94d529a6209bcb82ef3775d414f19d5678a
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>