There is no connection whatsoever between the vSphere Foundations exam and any of the VCA certifications.
Foundations is a core exam for all the VCP6/VCP7 certifications.
I don't personally think VCA certifications have value, so would suggest you proceed with the Foundations exam followed by 2V0-731 - once you've passed both you'll be VCP7-CMA certified, so long as you've also met any training requirement for VCP7-CMA.