[x86][inline-asm] Introducing (AVX512) k0-k7 registers for inline-asm usage

 Commit on behalf of mharoush

 After LGTM and check all:
 This patch enables usage of k registers in inline assembly syntax.
 Adding triple

 Reviewer: 1. rnk
           2. delena

 Differential Revision: https://reviews.llvm.org/D25011

llvm-svn: 285563