nv30, nv40: unify all structures and headers, except shaders

nv30, nv40: unify all structures and headers, except shaders

This patch unifies nv[34]0_screen.h, nv[34]0_context.h and
nv[34]0_state.h

The unified files are put in a new "nvfx" directory.

nv30_context.h and nv40_context.h still exist to hold the function
prototypes and include nvfx_context.h

nv[34]0_screen.h and nv[34]0_state.h are deleted, replaced by the
unified versions.

nv40 includes some extra fields for swtnl and user clip planes
support.

These fields will be unused on nv30 until that functionality gets
added to it too (by unification with nv40).