The CPU is "good enough" because most games are dependent on the GPU, not the CPU. However, it depends on the game you want to play since there are games that can use more than 2 cores. The Radeon HD 8670m is a bit dated though and is rather weak, it is basically in between the nVidia 910m and 920m. The Intel HD 620 is ranked within the same range.
I have an old Dell Latitude 3540 laptop with the i5-4200u and the more powerful Radeon HD 8850m which is roughly equal or slightly better than the nVidia 940mx. It serves as a secondary laptop nowadays. I kinda stopped playing games... or more precisely the only game I have been playing for about the past year is Star Trek Online (STO). Having said that, I can run Fallout 4 on my laptop decently well at 1080p with a mix of low and medium settings. Fallout 4 is both CPU and GPU intensive. I probably could have gotten better FPS if I had quad core CPU, but definitely it would not be as good as having a more powerful GPU.
There are games that you can play but your biggest bottleneck will be the Radeon HD 8670m. STO is an example of a game that you can play even with the integrated Intel HD 4400 graphics core; it is a free to play game. But if you are thinking about playing games like GTA V or Battlefield, then you would be pretty disappointed by the performance or lack of performance you will get.
Below is a link to game benchmarks on the Intel HD 620 graphics core in 7th generation Intel CPUs and is considered to be a little more powerful than the Radeon HD 8670m.