[X86][SSE] Use the general SMAX/SMIN/UMAX/UMIN opcodes and remove the X86 implementation

With the completion of D9746 there is now a common implementation of integer signed/unsigned min/max nodes, removing the need for the equivalent X86 specific implementations.

This patch removes the old X86ISD nodes, legalizes the relevant SSE2/SSE41/AVX2/AVX512 instructions for the ISD versions and converts the small amount of existing X86 code.

Differential Revision: http://reviews.llvm.org/D10947

llvm-svn: 241506