i2c: Add support for the TSL2550

Add support for Taos TSL2550 ambient light sensors.
(http://www.taosinc.com/product_detail.asp?cateid=4&proid=18

).

Signed-off-by: Rodolfo Giometti <giometti@linux.it>
Signed-off-by: Jean Delvare <khali@linux-fr.org>