odroid: defconfig: disable memset at malloc init

odroid: defconfig: disable memset at malloc init

Reduce the boot time of Odroid X2/U3 by disabling the memset
at malloc init.

This was tested on Odroid X2.
A quick test with checking gpio pin state using the oscilloscope.
Boot time from start to bootcmd (change gpio state by memory write command):
- ~228ms - before this change (arch memset enabled for .bss clear)
- ~100ms - after this change

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Reviewed-by: Simon Glass <sjg@chromium.org>