Actually ARM has small direct competition on the market. I can only think of Imagination technologies and Vivante Corporation as direct competitors of ARM in the IP GPU arena.2016 is a long ways away still. I'm sure the competition will have at least the same as well. Heck, Intel may even be knocking on their power/performance door by that point.
Intel doesn't license it's IP blocks to AMD. AMD only has an ISA license, but has to design its own processors (implementing x86). That is not the case with ARM that sells fluull processor blocks or in that case a GPU block for other to use in their own socs.If that was the case, then AMD wouldn't be considered a competitor to Intel since Intel licenses out the x86 IP to them.
The Mali GPU is only used only in certain lines of ARM chips. While you mentioned Vivante (not sure who uses it) and Imagination technologies (PowerVR used by Apple), there's also Qualcomm's Adreno, Nvidia's Tegra, and Broadcom's VideoCore; among others.