dt-bindings: extcon: Add support for SM5502 MUIC device

This patch add documentation for binding of SM5502 MUIC (Micro-USB Interface
Controller) device which is using EXTCON subsystem. The SM5502 MUIC device
can detect various external accessories when external accessories is attached
or detached.

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>