Reduce spi-max-frequency for ipTIME A8004T and disable
m25p,fast-read option.
In this case, openwrt can't detect the partition information,
it would write the inccorect data to the firmware partition and
also it would occur the bootlooping after sysupgrade.
Signed-off-by: Sunguk Lee <d3m3vilurr@gmail.com>
[minor commit title/message adjustments]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
