Documentation/process: Add embargoed HW contact for LLVM

Should the need for toolchain mitigations ever be necessary, add a group
for toolchain ambassadors.

Add Nick Desaulniers as LLVM's ambassador for the embargoed hardware
issues process.

Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20220711181101.1559558-1-ndesaulniers@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>