AVX-512: Removed "z" suffix from AVX-512 instructions, since it is incompatible with...

AVX-512: Removed "z" suffix from AVX-512 instructions, since it is incompatible with GCC.
I moved a test from avx512-vbroadcast-crash.ll to avx512-vbroadcast.ll
I defined HasAVX512 predicate as AssemblerPredicate. It means that you should invoke llvm-mc with "-mcpu=knl" to get encoding for AVX-512 instructions. I need this to let AsmMatcher to set different encoding for AVX and AVX-512 instructions that have the same mnemonic and operands (all scalar instructions).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197041 91177308-0d34-0410-b5e6-96231b3b80d8