avx512 implementation fixes and next steps

git-svn-id: svn://svn.code.sf.net/p/bochs/code/trunk@11867 6c8e4198-a580-4521-a02f-c9ae86df1db9
opmask_ok support in fetchdecode32.cc

git-svn-id: svn://svn.code.sf.net/p/bochs/code/trunk@11868 6c8e4198-a580-4521-a02f-c9ae86df1db9