i965: Fix message and response length calculations for INT DIV.

i965: Fix message and response length calculations for INT DIV.

Both POW and INT DIV need a message length of 2; previously, we only
checked for POW.

Also, BRW_MATH_FUNCTION_INT_DIV_QUOTIENT_AND_REMAINDER has a response
length of 2; previously, we only checked for SINCOS.  We don't use this
message, but in case we ever decide to, we may as well fix it now.

While we're at it, just move these computations into
brw_set_math_message, since they're entirely based on the function.
This fixes it for both brw_math and the old backend's brw_math_16.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Tested-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>