i965: Fix RNDZ and RNDE on Sandybridge and Ivybridge.

i965: Fix RNDZ and RNDE on Sandybridge and Ivybridge.

On gen4/5, the RNDZ and RNDE instructions return floor(x), but set special
"round increment bits" in the flag register; a predicated ADD (+1) fixes
the result.

The documentation still lists '.r' as existing, and says that the
predicated add is necessary, but it apparently lies.  According to the
simulator, BRW_CONDITIONAL_R (7) is not a valid conditional modifier
and the RNDZ and RNDE instructions simply produce the correct value.

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