[SKX] avx512_icmp_packed multiclass extension
Extended avx512_icmp_packed multiclass by masking versions.
Added avx512_icmp_packed_rmb multiclass for embedded broadcast versions.
Added corresponding _vl multiclasses.
Added encoding tests for CPCMP{EQ|GT}* instructions.
Add more fields for X86VectorVTInfo.
Added AVX512VLVectorVTInfo that include X86VectorVTInfo for 512/256/128-bit versions

Differential Revision: http://reviews.llvm.org/D5024