I'm not sure that AMD does this, but for Intel graphics, the VRAM is half of the RAM so assuming AMD does similarly, and I am not sure it does, it would have half the RAM tied up for graphics. It also is using CPU cores instead of CUDA cores like the 940 does. The amount of VRAM makes a slight difference but it's not everything.
Honestly If you have the option to go with a dedicated graphics card do it. You can take Intel HD 630, which is the Kaby Lake integrated graphics, and compare it with the 1050, a budget $100 card, and the 1050 beats it by over 250%. Even the 940m beats the brand new 2017 top of the line HD 630 by a few percent, so a mobile year old, x40 card, beats arguably the best integrated graphics in existence, which I cant confirm since I can't find any kind of benchmarks on the a12 so I really can't tell you more about that specifically.
Just that in general, dedicated graphics are better.