pinctrl: Add sleep related state to indicate sleep related configs

In some scenarios, we should set some pins as input/output/pullup/pulldown
when the specified system goes into deep sleep mode, then when the system
goes into deep sleep mode, these pins will be set automatically by hardware.

That means some pins are not controlled by any specific driver in the OS, but
need to be controlled when entering sleep mode. Thus we introduce one sleep
state config into pinconf-generic for users to configure.

Signed-off-by: Baolin Wang <baolin.wang@spreadtrum.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>