Revert "kernel: Remove unneeded MKDTIMG dependency"

This reverts commit caa3bddf.

Reason for revert: Breaks pixel dtbo.img build, since kernel depends on
mkdtimg. Add it back so it gets compiled and kernel can pick it up.

Change-Id: I2b9fd0b2b35e0cf2f908516b10f65399780d5c30