Split Atari 2600 hash into a NTSC & PAL version

The PAL roms do not run well on NTSC (a2600), because the bottom part of the game falls off screen. I created a second hash file for these cartridges.

- The a2600p is an official MESS system for PAL roms.

- I have tested the hashes in MAMEHub and they seem to be working fine.

PS: I do not know if the remaining roms in a2600.hsi are all NTSC, but it is an improvement nonetheless.