imx: Guard print_cpuinfo with !CONFIG_IS_ENABLED(CPU)

imx: Guard print_cpuinfo with !CONFIG_IS_ENABLED(CPU)

When CONFIG_CPU is enabled, print_cpuinfo is defined in common/board_f.c
with static property. However in imx cpu.c, print_cpuinfo is not a local
function, so guard it with !CONFIG_IS_ENABLED(CPU).

And all i.MX8M boards has CONFIG_CPU and CONFIG_CPU_IMX set, so remove the
dead code.

However legacy print_cpuinfo also print reset reason, to keep reset
reason printed as before, export get_reset_reason() and invoke it
at arch_misc_init().

Signed-off-by: Peng Fan <peng.fan@nxp.com>