i686: Use generic sincosf implementation for SSE2 version

The generic implementation shows slight better performance
(gcc 11.2.1 on a Ryzen 9 5900X):

* s_sincosf-sse2.S:
  "sincosf": {
   "workload-random": {
    "duration": 3.89961e+09,
    "iterations": 9.5472e+07,
    "reciprocal-throughput": 40.8429,
    "latency": 40.8483,
    "max-throughput": 2.4484e+07,
    "min-throughput": 2.44808e+07
   }
  }

* generic s_cossinf.c:
  "sincosf": {
   "workload-random": {
    "duration": 3.71953e+09,
    "iterations": 1.48512e+08,
    "reciprocal-throughput": 25.0515,
    "latency": 25.0391,
    "max-throughput": 3.99177e+07,
    "min-throughput": 3.99375e+07
   }
  }

Checked on i686-linux-gnu.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>