i965: Introduce a new SHADER_OPCODE_URB_READ_SIMD8 opcode.

i965: Introduce a new SHADER_OPCODE_URB_READ_SIMD8 opcode.

In scalar mode, geometry shader inputs can easily take up hundreds of
registers.  This makes pushing VUE entries impractical; we'll need to
resort to the pull model in some cases.

To support this, we introduce a new opcode corresponding to the "URB
Read SIMD8" message.

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