i386: Remove TARGET_VECTORIZE_BUILTIN_CONVERSION.

i386: Remove TARGET_VECTORIZE_BUILTIN_CONVERSION.

Renaming all of the insn patterns as needed to the standard
optab forms.  Sadly, only one of the builtins is unused by
the various header files, so most of them must stay around.

        * config/i386/sse.md (floatv8siv8sf2): Rename from avx_cvtdq2ps256.
        (floatv4siv4sf2): Rename from sse2_cvtdq2ps.
        (floatunsv4siv4sf2): Rename from sse2_cvtudq2ps.
        (fix_truncv8sfv8si2): Rename from avx_cvttps2dq256.
        (fix_truncv4sfv4si2): Rename from sse2_cvttps2dq.
        (floatv4siv4df2): Rename from avx_cvtdq2pd256.
        (fix_truncv4dfv4si2): Rename from avx_cvttpd2dq256.
        (vec_unpacku_float_hi_v8si): Update for insn pattern name changes.
        * config/i386/i386.md (splitters for int-float conversion): Likewise.
        * config/i386/i386.c (ix86_split_convert_uns_si_sse): Likewise.
        (bdesc_args): Likewise.
        (enum ix86_builtins) [IX86_BUILTIN_CVTUDQ2PS]: Remove.
        (ix86_vectorize_builtin_conversion): Remove.
        (TARGET_VECTORIZE_BUILTIN_CONVERSION): Remove.

From-SVN: r180709