MLK-19697 imx6sx sd board emmc config should use emmc kernel dtb default

change default dtb to imx6sx-sdb-emmc.dtb when config as emmc

Signed-off-by: Frank Li <Frank.Li@nxp.com>
(cherry picked from commit 695f522c07f5cec82e5c53f35fb58c0d763d0054)
1 file changed