AM3517: rename the i2c boardinfo to make it more readable

There are three i2c buses on am3517, and each i2c bus has several devices
on it, so we can't name the i2c boardinfo structures with one of these
devices. In order to make it more readable, now rename these three boardinfo
structures based on i2c indexes.

Signed-off-by: Stanley.Miao <stanley.miao@windriver.com>
Acked-By: Vaibhav Hiremath <hvaibhav@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>