[PATCH v4] x86: vm86 cleanups

[Brian Gerst <brgerst@gmail.com>]

The goal of this set of patches is to change vm86 support to return to
userspace with the normal exit paths instead of leaving data on the kernel
stack and jumping directly into the exit asm routines.  This fixes issues
like ptrace and syscall auditing not working with vm86, and makes possible
cleanups in the syscall exit work code.

Changes from v3:
- Removed patches already accepted
- Renamed some fields per Ingo
- Added patches to allow disabling hardware IRQ support and to fix includes
- Added helper macro for free_vm86 (Note: could not use inline function due
  to header issues)

Changes from v2:
- Use gs slot of regs32 (present but unused in lazy mode)
- Add access_ok() checks before get_user_try/put_user_try

Changes from v1:
- Added first two patches
- Changed userspace access to copy each field explicitly instead of relying
  on the same order of members in the structure.