ARM: dts: msm8974: Further reduce retention voltages

* Based on @faux123 's commit: https://github.com/faux123/Nexus_5/commit/0588c11de20c19d64dc25c0bafda7aa4e7ffbd66
* Further reducing retention voltage for non-boot CPUs

Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
defconfig: Enable IOMMU VBIF check

Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>