i965: Make a brw_stage_prog_data for storing the SURF_INDEX information.

i965: Make a brw_stage_prog_data for storing the SURF_INDEX information.

It would be nice to be able to pack our binding table so that programs
that use 1 render target don't upload an extra BRW_MAX_DRAW_BUFFERS - 1
binding table entries.  To do that, we need the compiled program to have
information on where its surfaces go.

v2: Rename size to size_bytes to be more explicit.

Reviewed-by: Paul Berry <stereotype441@gmail.com>