Welcome to the world of misfit toys (
https://www.youtube.com/watch?v=LFDccEaBHQU)
I hate to be the bearer of bad news, but development requires developers, and that requires either; cash, or something interesting to work on. Or both. So how much money do you have?
On a more practical note, you will at the very least have to:
1) Get a schematic of the device, download all of the spec sheets, manuals, app notes, errata, etc for every last stinking chip (CPU, GPU, Controller, down to the lowliest UART chip).
2) Read all of the aforementioned documentation (that'll keep you busy for awhile).
3) Using the linux kernel sources as a guide (all 28 gazillion megs of it...), develop your kernel, drivers, & programs for your hardware.
3a) Maybe you should stop here as well :
https://www.google.com/webhp?source=...es&safe=active
4) Take it apart and locate the JTAG interface. It will succumb to your modifications (in other words, blast the sucker with your new code). Whether it works after that is a different story...
4a) Do all of the steps that I invariably left out.
5) Profit!!
Besides, I was here first! You need to wait your turn until linux gets ported to my Apple Newton!