Here's the currently available documentation for the Cortex A8 core.
Cortex-A8 Technical Reference Manual (r2p3)(PDF)
This is the canonical reference to the Cortex A8 architecture. It references the ARM Architecture Reference Manual
quite a bit, and both documents include details on the ARM7, Thumb and VFP components to the Cortex A8 processor used in the i.MX515.
Right now documentation on the NEON media processing unit is somewhat restricted to those two documents, as the technical reference for the NEON unit is still under confidentiality agreements. We will work on this with Freescale and ARM so that we can provide Project Developers with the appropriate documentation. There is a page in the gcc manual for the NEON intrinsics
which should serve as a useful reference in the meantime.
Please watch for updates to this thread, and when everything solidifies we will put up a dedicated set of Platform Support
pages containing all this and more.