defconfig: sdmsteppeauto: Enable dm-init module

From the kernel 5.1, added a "dm-mod.create" kernle cmdline parameter,
which allows device-mapper targets to be configured at boot time.
This enables early use of DM targets in the boot process (as the root
device or otherwise) without the need of an initramfs. So enabled the
dm-init module for dm-verity.

Change-Id: I0566666894d56bb9f752d2dfa0f6717b0a26a0a4
Signed-off-by: Nan Zhang <nanzhan@codeaurora.org>