Update specified 74xx logic chips.

[thorpej]

Per discussion on Discord, it would probably be worth updating the BOM to clarify which 74xx logic families are best for which ICs. In particular:

• The GPIO-in 74xx244 does need to receive 5V TTL signals, because that will be sufficient to receive the 3V3 CMOS MISO signal from the SD card. Substituting a 74HCT244 would result in similar performance and lower power consumption over the 74LS244.
• Per episode 10a in the YT playlist, the glue logic for the flash interface could probably benefit from some extra margin. For this reason, substituting a 74AHC32 for the 74HC32 might be a good choice. The performance of there other 74xx32 isn't as critical, but specifying both as 74AHC32 simplifies the BOM with basically no cost penalty.
• All other 74xx logic can be HC family -- speed is not a concern for these other applications, and HC is generally preferred over HCT for its reduced vulnerability to noise.

I am planning to build my board this way, and will update this issue with the results.