Revert "Remove comments and code about ro.boot.slot"

This reverts commit f4ec2c50a3d2fec6d2d95f9259d9c44900977748.

Dependencies hadn't been merged yet.

Bug: 66437505
Change-Id: I7551b7f2f184a6fefc39e184a42dc8d323c58b89
2 files changed