defconfig: sm8150: Enable auto onlining of hotplug memory blocks

Auto online the memory blocks after being added. Also, by default
these blocks will be added to ZONE_MOVABLE zone.

Change-Id: Ibdcccdf01491f04ec88f05571b1e34365cf5e6ea
Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org>