defconfig: arm: msm: enable vmalloc saving on msm8917/20/37/40

For some targets that have less vmalloc space, increase the size by
enabling the vmalloc_savings option. Config ENABLE_VMALLOC_SAVING reclaims
virtual mappings which remains unused because of non hlos carveout
reservations in lowmem.

Change-Id: I04d75852ef2eabb855f7886c336e9778164a5b6a
CRs-Fixed: 2112076
Signed-off-by: Swetha Chikkaboraiah <schikk@codeaurora.org>