defconfig: msm8994: enable vbif check to debug various iommu issues

VBIF check is used to extract VBIF's client information whenever iommu
tlb sync, iommu halt or vbif related issues are observed. VBIF register
dump is collected into kernel logs which assist iommu related debugging.

Change-Id: I2263ea94a83e5a3c758328e2900e859baed254bd
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>