The Vivante Mesa Driver Is Still Brewing
Among the ARM SoCs with the Vivante GPU are many of the Marvell Armada chips along with the Freescale i.MX6 and the Actions ATM7029 and Rockchip 2918. There's also the MIPS-based Ingenic JZ4760/JZ4770 that boast Vivante GPU cores.
The current state of the Vivante "etnaviv" Mesa driver is that it's capable of OpenGL ES 1.0 and 2.0 accelerated rendering directly to a frame-buffer (fbdev) device. According to the developers, this reverse-engineered driver can run GLQuake, the DarkPlaces engine, and other OpenGL ES games.
While the user-space Mesa driver has progressed, sadly it's not mainline and hasn't seen much activity as of late. The Etnaviv Mesa Git repository hasn't been synced now in two months. The code from which the driver is targeting is an old snapshot of Mesa 9.3.0-devel from about five months ago.
The other upstream source for the Etnaviv driver work is this Git repository where plenty more information on the driver and the reverse-engineering work is documented. The latest activity here is from one month ago.
While progress has slowed as of late and the driver hasn't been mainlined yet, hopefully it will catch up to speed in 2014. If you are looking for an ARM GPU with open-source graphics support, I would easily recommend going the Qualcomm Adreno route with the Freedreno driver. Rob Clark has not only written a Gallium3D driver for the Qualcomm ARM SoCs through reverse-engineering and has mainlined the code and maintained it for months, his latest adventure was writing a DRM/KMS driver that is also now mainline and based upon Qualcomm's open-source Android kernel driver. Freedreno is where the most exciting open-source ARM graphics work is happening at the moment.