It would be great if someone could scour the web for more information about the various compute units in modern SoCs.
AMD explains some of heterogeneous systems architecture here: http://developer.amd.com/resources/heterogeneous-computing/what-is-heterogeneous-system-architecture-hsa/
I was reading about OMAP 5, a System-on-Chip designed by Texus Instrument using ARM components (technical document here: http://www.ti.com/pdfs/wtbu/SWCT010.pdf). This was the last generation of SoC from TI, as they decided to shift from mobile to embedded platform back in 2012 and essentially cut the OMAP project.
The chip features dual-core ARM Cortex-A15 CPU and two Cortex-M4 cores for less intensive tasks (this is an example of heterogeneous computing for power efficiency). It also contains two PowerVR SGX544MP graphics cores, along with support for camera, memory, HD display, USB ports, and SATA controller.
For people who still remember the Nokia era (e.g. N9, N95 Symbian phones), in fact OMAP was used in them! It's good to finally know what powered them after all these years.