pinctrl&gpio: add new interface to set pull-down/up

pinctrl&gpio: add new interface to set pull-down/up

PD#142470: pinctrl&gpio: add new interface to set pull-down/up

1. add property file 'pull' in directory /sys/class/gpio/gpioX/
pull-up:      echo up > pull
pull-down:    echo down > pull
pull-disable: echo disable > pull

2. add new functions, as follows:
+ gpiod_set_pull(struct gpio_desc *desc, int value)
+ gpiod_set_pull_cansleep(struct gpio_desc *desc, int value)

'value' can be set:
GPIOD_PULL_DIS
GPIOD_PULL_DOWN
GPIOD_PULL_UP

Change-Id: Iba750729288651a897ebac827093ebc6c143f16b
Signed-off-by: xingyu.chen <xingyu.chen@amlogic.com>