ADD support for freescale i.MX6

Hi 

Here is a PR (split as 2 commits to ease reviewing) which adds support for the Freescale i.MX6 SystemOnChip.
I initiated this work a little more than one year ago in this [thread](http://forum.xbmc.org/showthread.php?tid=161793). Then, to ease collaboration, this porting effort moved to github [repo](https://github.com/xbmc-imx6/xbmc) when Chris contributed the rendering through vivante extensions.

This result is a collaborative work and I would like to thank especially @koying, @smallint and @warped-rudi who helped a lot with this development. Also maintainers of Geexbox, archlinux arm and openelec helped a lot.

This code is known to work on all i.MX6 variants and has been run successfully on a large number of boards/devices.

Sorry if everything is not ready for inclusion : I am fully available to take into account all your remarks or to provide explanations to enable this merge.

Stéphan
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