i965/vs: move ARB_vertex_program functions to vec4_vs_visitor.

i965/vs: move ARB_vertex_program functions to vec4_vs_visitor.

This patch moves functions from vec4_visitor to vec4_vs_visitor that
deal with ARB (assembly) vertex programs.  There's no point in having
these functions in the base class since we don't intend to support
assembly programs for the GS stage.  The following functions are
moved:

- setup_vp_regs
- get_vp_dst_reg
- get_vp_src_reg

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>