Revert "writeback: I believe these defines were calculated with HZ=1000 in mind. Since our devices are HZ=100 I hardcoded the values on this constants. I'm not 100% sure if this code was made for HZ with 1000 but I couldn't track it to understand clearly. Although I didn't see any drawback of using this as it is now. If anyone knows the answer please chime in."

This reverts commit fab7e959ff798466b493ff90e2248078ae37a2dc.
arch: arm: boot: Makefile: Add clean step for zImage-dtb