Implement mmx_pblendv to optimize V8HI, V4HI and V2SI mode
conditional moves for SSE4.1 targets.

2021-05-07  Uroš Bizjak  <ubizjak@gmail.com>

gcc/
    PR target/98218
    * config/i386/i386-expand.c (ix86_expand_sse_movcc):
    Handle V8QI, V4HI and V2SI modes.
    * config/i386/mmx.md (mmx_pblendvb): New insn pattern.
    * config/i386/sse.md (unspec): Move UNSPEC_BLENDV ...
    * config/i386/i386.md (unspec): ... here.

Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.

Pushed to master.

Uros.