nv30, nv40: non-trivially unify nv[34]0_vertprog.c

nv30, nv40: non-trivially unify nv[34]0_vertprog.c

vertprog.c is similar but has substantial differences:
1. nv40 supports clip planes
2. nv40 uses a more advanced register allocator
3. Some register setup is different
4. Constants with the same name have different values

This patch unifies the two files.
nv30 gains clip plane support and the nv40 register allocator.

A new NVFX_VP(x) macro is introduced that at runtime resolved to
either the nv30 or the nv40 constant value.

nv30 clip planes are not tested and might not work