fix(dm): add rootfs-block as a dependency to dm module

[LaszloGombos]

Supporting dm without rootfs-block not tested configuration. I do not see use case to support dm module without rootfs-block.

The main intent of this PR is to simplify code for maintenance and improve dependency management.

After this PR dracut -m dm will actually produce a bootable initramfs with rootfs-block included.

[stale]

This issue is being marked as stale because it has not had any recent activity. It will be closed if no further activity occurs. If this is still an issue in the latest release of Dracut and you would like to keep it open please comment on this issue within the next 7 days. Thank you for your contributions.

[stale]

This issue is being marked as stale because it has not had any recent activity. It will be closed if no further activity occurs. If this is still an issue in the latest release of Dracut and you would like to keep it open please comment on this issue within the next 7 days. Thank you for your contributions.

[stale]

This issue is being marked as stale because it has not had any recent activity. It will be closed if no further activity occurs. If this is still an issue in the latest release of Dracut and you would like to keep it open please comment on this issue within the next 7 days. Thank you for your contributions.