i965/vs: move VS-specific data members to vs_vec4_visitor.

i965/vs: move VS-specific data members to vs_vec4_visitor.

This patch moves the following data structures from vec4_visitor to
vec4_vs_visitor, since they contain VS-specific data:

- struct brw_vs_compile *c (renamed to vs_compile)
- struct brw_vs_prog_data *prog_data (renamed to vs_prog_data)
- src_reg *vp_temp_regs
- src_reg vp_addr_reg

Since brw_vs_compile and brw_vs_prog_data also contain vec4-generic
data, the following pointers are added to the base class, to allow it
to access the vec4-generic portions of these data structures:

- struct brw_vec4_compile *c
- struct brw_vec4_prog_key *key
- struct brw_vec4_prog_data *prog_data

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
v2: Use shorter names in the base class and longer names in the
derived class.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>