dm: Restore reverted changes

This is a preparation change for merging android-4.14-q.133 into
msm-4.14 branch.

The following changes need to be reverted, otherwise boot
stuck on rootfs mount:

ba7dee4c Revert "CHROMIUM: dm: boot time specification of dm="
cf193eee Revert "ANDROID: dm: do_mounts_dm: Rebase on top of 4.9"
13c4f91f Revert "ANDROID: dm: do_mounts_dm: fix dm_substitute_devices()"
321a9efa Revert "ANDROID: dm: do_mounts_dm: Update init/do_mounts_dm.c to the latest ChromiumOS version."

The above reverted changes are required when 'system is root'
and the mount instructions (including dm-verity) for system
image is provided by the bootloader through the kernel cmdline
even with AVB 2.0. Dynamic/Super partition has not been enabled
internally which will ensure system image is mounted by early
init. Since this will only be supported for new launches of Q,
still these changes are required to be present for OTA devices.

Change-Id: Ie6c093cdd2d1dc1e578ebce06b3923f81c06ed6f
Signed-off-by: Blagovest Kolenichev <bkolenichev@codeaurora.org>