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 <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt

···
 			  (such as enabling an output buffer)
 output-low		- set the pin to output mode with low level
 output-high		- set the pin to output mode with high level
+sleep-hardware-state	- indicate this is sleep related state which will be programmed
+			  into the registers for the sleep state.
 slew-rate		- set the slew rate
 
 For example:

drivers/pinctrl/pinconf-generic.c

···
 	PCONFDUMP(PIN_CONFIG_OUTPUT_ENABLE, "output enabled", NULL, false),
 	PCONFDUMP(PIN_CONFIG_OUTPUT, "pin output", "level", true),
 	PCONFDUMP(PIN_CONFIG_POWER_SOURCE, "pin power source", "selector", true),
+	PCONFDUMP(PIN_CONFIG_SLEEP_HARDWARE_STATE, "sleep hardware state", NULL, false),
 	PCONFDUMP(PIN_CONFIG_SLEW_RATE, "slew rate", NULL, true),
 };
 
···
 	{ "output-high", PIN_CONFIG_OUTPUT, 1, },
 	{ "output-low", PIN_CONFIG_OUTPUT, 0, },
 	{ "power-source", PIN_CONFIG_POWER_SOURCE, 0 },
+	{ "sleep-hardware-state", PIN_CONFIG_SLEEP_HARDWARE_STATE, 0 },
 	{ "slew-rate", PIN_CONFIG_SLEW_RATE, 0 },
 };
 

include/linux/pinctrl/pinconf-generic.h

···
  * @PIN_CONFIG_POWER_SOURCE: if the pin can select between different power
  *	supplies, the argument to this parameter (on a custom format) tells
  *	the driver which alternative power source to use.
+ * @PIN_CONFIG_SLEEP_HARDWARE_STATE: indicate this is sleep related state.
  * @PIN_CONFIG_SLEW_RATE: if the pin can select slew rate, the argument to
  *	this parameter (on a custom format) tells the driver which alternative
  *	slew rate to use.
···
 	PIN_CONFIG_OUTPUT_ENABLE,
 	PIN_CONFIG_OUTPUT,
 	PIN_CONFIG_POWER_SOURCE,
+	PIN_CONFIG_SLEEP_HARDWARE_STATE,
 	PIN_CONFIG_SLEW_RATE,
 	PIN_CONFIG_END = 0x7F,
 	PIN_CONFIG_MAX = 0xFF,