[docs] Improved file-level documentation for src/cpu_dep.c. Added several comments to explain some of the tricker or more esoteric features of that file. Removed outdated file references.
[docs] Improved file-level documentation for src/cpu_dep.c. Added several comments to explain some of the tricker or more esoteric features of that file. Removed outdated file references.

git-svn-id: 6e74a02f85675cec270f5d931b0f6998666294a3@28857 d31e2699-5ff4-0310-a27c-f18f2fbe73fe

ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot