arm/imx6: add imx6q sabrelite board support

- Add basic board dts file
- Add board compatible string to mach-imx6q.
- Update fsl DT board doc.

Signed-off-by: Richard Zhao <richard.zhao@linaro.org>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/mach-imx/mach-imx6q.c

@@ -73,6 +73,7 @@ static struct sys_timer imx6q_timer = {
 
 static const char *imx6q_dt_compat[] __initdata = {
 	"fsl,imx6q-sabreauto",
+	"fsl,imx6q-sabrelite",
 	NULL,
 };