Upstreaming avx512 register support in debugserver. These changes

were originally written by Chris Bieneman, they've undergone a
number of changes since then.

Also including the debugserver bridgeos support, another arm
environment that runs Darwin akin to ios.  These codepaths are
activated when running in a bridgeos environment which we're not
set up to test today.

There's additional (small) lldb changes to handle bridgeos binaries
that still need to be merged up.

Tested on a darwin system with avx512 hardware and without.

<rdar://problem/36424951> 

llvm-svn: 326756