i965: Convert 3DPRIMITIVE command from struct-style to OUT_BATCH style.

i965: Convert 3DPRIMITIVE command from struct-style to OUT_BATCH style.

Most of the newer portions of the code use OUT_BATCH style.  I prefer
this style because it offers a clear distinction between a) hardware
messages/structures with a mandatory format, and b) data structures for
our own internal use that we can format however we want.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>