uboot-sunxi: disable AXP209 on Olimex A13 Olinuxino

uboot-sunxi: disable AXP209 on Olimex A13 Olinuxino

Disable the PMIC on Olimex A13 Olinuxino, as the SPL cannot set the
core voltage correctly, which causes the board to freeze later at
kernel if CPU throttling is enabled (see below). This will almost
certainly kill the VGA output (which requires LDO3 to be set), but
this is still a better option than to disable CPU throttling for
all Cortex-A8 based devices.

[    2.485632] cpufreq: cpufreq_online: CPU0: Running at unlisted freq: 384000 KHz
[    2.525698] cpufreq: cpufreq_online: CPU0: Unlisted initial frequency changed to: 432000 KHz

Signed-off-by: Zoltan HERPAI <wigyori@uid0.hu>