i965: Rename brw_vec4_prog_data/key to brw_bue_prog_data/key

i965: Rename brw_vec4_prog_data/key to brw_bue_prog_data/key

These structs aren't vec4 specific, they are shared by shader stages
operating on Vertex URB Entries (VUEs).  VUEs are the data structures in
the URB that hold vertex data between the pipeline geometry stages.
Using vue in the name instead of vec4 makes a lot more sense, especially
when we add scalar vertex shader support.

Signed-off-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>