ARM: dts: apq8064: rename db600c to SD_600eval

This board has been renamed recently and announced at
https://eragon.einfochips.com/products/sd-600eval.html



So rename this board files so that it reflects actual product in market.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>