powerpc u-boot fdt修正过程。

do_bootm---------------->boot_body_linux -------------->ft_board_setup

1、mac地址修正：u-boot修正：fdt_fixup_ethernet,     kernel内部修正mac地址：of_get_mac_address

2、获取cpu频率：const u32 *max_freqp; 

                                 u32 max_freq;

                                 max_freqp = of_get_property(cpu, "clock-frequency", NULL);

                                 max_freq = *max_freqp / 1000;