dt-bindings: extcon: Add support for fsa9480 switch

This patch adds documentation for binding of extcont Fairchild
Semiconductor FSA9480 microusb switch.
This usb port accessory detector and switch, can be found for example in
some Samsung s5pv210 based phones.

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
Signed-off-by: Paweł Chmiel <pawel.mikolaj.chmiel@gmail.com>
Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>