i965/fs: Drop the generate_math[12]_gen7 methods.

i965/fs: Drop the generate_math[12]_gen7 methods.

These functions are basically identical, so we should combine them.
However, they're so trivial, we may as well just fold them into their
only call sites.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>