R600/SI: implement range reduction for sin/cos

These instructions can only take a limited input range, and return
the constant value 1 out of range. We should do range reduction to
be able to process arbitrary values. Use a FRACT instruction after
normalization to achieve this. Also add a test for constant folding
with the lowered code with unsafe-fp-math enabled.

v2: use DAG lowering instead of intrinsic, adapt test
v3: calculate constant, fold pattern into instruction definition
v4: misc style fixes, add sin-fold testcase, cosmetics

Patch by Grigori Goronzy