Partially revert "Assume sensors perform prox check"

This commit partially reverts f40bd8fb
("Assume sensors perform prox check").

Some devices do not have proximity gated sensors, and still require
gating in software.
Partially revert this commit to bring back the ability for sensors to
be proximity gated in software.

Change-Id: Ic3d5c6e98d1767623ace4ee4eea1c52606fabd4a