1. undefine led_classdev_register as it is defined in leds.h
2. header file location change
a. linux/i2c/pmbus.h -> linux/pmbus.h
b. linux/i2c-mux-gpio.h -> linux/platform_data/i2c-mux-gpio.h
c. linux/i2c/pca954x.h -> linux/platform_data/pca954x.h
* [MultiDB] (except ./src and ./dockers dirs): replace redis-cli with sonic-db-cli and use new DBConnector
* update comment for a potential bug
* update comment
* add TODO maker as review reqirement