adc_keypad: update interface to access adc and add sysfs interface

adc_keypad: update interface to access adc and add sysfs interface

PD#146614: adc_keypad: update interface to access adc and add sysfs interface

1.use sysfs interface to set dynamic key
inquire key map:
cat /sys/devices/platform/adc_keypad/table

set key:
echo [name]:[code]:[channel]:[value]:[tolerance] >
			/sys/devices/platform/adc_keypad/table

2. use the consumer interface of the IIO to access sar adc

Change-Id: I0357e84720340b0fee4baa882f41f0aa7f36a9a1
Signed-off-by: xingyu.chen <xingyu.chen@amlogic.com>