defconfig: Enable config to allow vmalloc savings

Enable the config ENABLE_VMALLOC_SAVING to reclaim
virtual mappings which remains unused because of
non hlos carveout reservations in lowmem.

Change-Id: Ic54049026fcdd99e47c8ec6b47d4aeb2649e80b0
Signed-off-by: Susheel Khiani <skhiani@codeaurora.org>