i965: Switch to the EU emit layer for code generation on Broadwell.

i965: Switch to the EU emit layer for code generation on Broadwell.

Everything should be in place to unify code generation between Gen4-7
and Gen8+.  We should be able to drop the Gen8 generators at this point.

However, leave them hooked up for a brief moment, for testing and
comparison purposes.  Set GEN8=1 to use the old Gen8+ code generator
paths.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Matt Turner <mattst88@gmail.com>