imx: mx8m: add soc related settings and files

Add SoC level initialization code
 - arch_cpu_init
 - mmu table
 - detect cpu revision
 - reset cpu and wdog settings
 - timer init
 - wdog settings
 - lowlevel init to save/restore registers
 - a few dummy header file to avoid build failure
 - ft_system_setup

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