imx: mx6sxsabresd: add command and macros for boot m4 core

Introduce macros and command to support booting M4 core for
i.MX6SX SabreSD board.

Signed-off-by: Ye.Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
1 file changed