imx6sl-warp has SD2_RESET pin connected to the eMMC reset line,
so add this pin to the usdhc2 group.
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>