imx: add i.MX8M into Kconfig

Add i.MX8M into Kconfig, create a new folder mx8m
dedicated for i.MX8M.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>
Reviewed-by: Stefano Babic <sbabic@denx.de>
3 files changed