dm: Restore reverted changes

This is a preparation change for merging android-4.14.114 into
msm-4.14 branch.

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

efe83653 Revert "CHROMIUM: dm: boot time specification of dm="
afaef205 Revert "ANDROID: dm: do_mounts_dm: Rebase on top of 4.9"
357c3d31 Revert "ANDROID: dm: do_mounts_dm: fix dm_substitute_devices()"
71eb40b7 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>