x86 cleanups from the LTO tree

From: Andi Kleen
Date: Thu Dec 21 2017 - 19:28:24 EST

These are all the fixes for the x86 tree needed for LTO. They are strictly
not needed without LTO, but I believe they can be all considered cleanups
and documentation improvements and are valuable because of that.

The initconst/data fixes help generating correct section permissions in the
vmlinux ELF file.