hw/i2c/ppc4xx_i2c: Add reference to datasheet

It took me a while to find this model datasheet, since it is
an OCR scan. Add a reference to save other developers time.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Acked-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Corey Minyard <cminyard@mvista.com>
1 file changed