They have been hiring a lot of graphics people and putting a team together.
And another thing that most people are not really aware: Apple had a lot of saying in the architectural and design decisions of Imagination's GPUs that ended up on their iPhones. A good part of the development actually happened at Apple's offices with Imagination people flying over.
So they know what they are doing, they are very well familiar with Imagination's GPU and they are more than capable of developing their own thing from scratch.