anv: Add a new block-based batch emit macro

anv: Add a new block-based batch emit macro

This new macro uses a for loop to create an actual code block in which to
place the macro setup code.  One advantage of this is that you syntatically
use braces instead of parentheses.  Another is that the code in the block
doesn't even get executed if anv_batch_emit_dwords fails.

Acked-by: Kristian Høgsberg <krh@bitplanet.net>