Patch 1.08 retroactively awarded Cryo Pod points based on AVP that had previously been gained past the pre-1.06 total.
Patch 1.06 changed the game so that the max AVP level is 29, allowing 28 Cryo Pod unlocks. This allows you to unlock all current Cryo Pods in one playthrough.
The previous answer is left below for those using 1.05 or earlier
Only 19 can be obtained in a playthrough (You start at Level 1 Andromeda Viability, and get 1 point per level up to level 20), and all your Cryo Pod unlocks are lost on NG+ (as well as your viability level being reset to 1).
The recent patch fixed the glitch that displayed negative AVP at level 20, which confirmed that 20 is the max Viability rank we can currently obtain. It is unknown at this point if Future DLC will increase this cap, or potentially award extra Cryo Pod points outside of Viability level.