[AVX-512] Replace V_SET0 in AVX-512 patterns with AVX512_128_SET0. Enhance...

[AVX-512] Replace V_SET0 in AVX-512 patterns with AVX512_128_SET0. Enhance AVX512_128_SET0 expansion to make this possible.

We'll now expand AVX512_128_SET0 to an EVEX VXORD if VLX available. Or if its not, but register allocation has selected a non-extended register we will use VEX VXORPS. And if its an extended register without VLX we'll use a 512-bit XOR. Do the same for AVX512_FsFLD0SS/SD.

This makes it possible for the register allocator to have all 32 registers available to work with.

llvm-svn: 292004