[U-Boot] replacing do_reset with a custom one

[Richard Retanubun <RichardRetanubun@RuggedCom.com>]

Mike Frysinger wrote:
> 
> #ifdef's are the past.  weaks are in!
> 
> the Blackfin port already does:
> void board_reset(void) __attribute__((__weak__));
> ...
>     if (board_reset)
>         board_reset();
> ...
> 
> the bf537-stamp uses this to make sure some pins are driven low to workaround 
> weak pull ups in the hardware
> -mike

Thanks for the tip Mike! I've submitted patches for MPC83xx and MCF5271 architectures.
They lack cpu.h file though, so I made one, let's see what the maintainers says.

Thanks again,

- Richard