x86/asm/entry: Remove user_mode_ignore_vm86()

x86/asm/entry: Remove user_mode_ignore_vm86()

user_mode_ignore_vm86() can be used instead of user_mode(), in
places where we have already done a v8086_mode() security
check of ptregs.

But doing this check in the wrong place would be a bug that
could result in security problems, and also the naming still
isn't very clear.

Furthermore, it only affects 32-bit kernels, while most
development happens on 64-bit kernels.

If we replace them with user_mode() checks then the cost is only
a very minor increase in various slowpaths:

   text             data   bss     dec              hex    filename
   10573391         703562 1753042 13029995         c6d26b vmlinux.o.before
   10573423         703562 1753042 13030027         c6d28b vmlinux.o.after

So lets get rid of this distinction once and for all.

Acked-by: Borislav Petkov <bp@suse.de>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Andrew Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brad Spengler <spender@grsecurity.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150329090233.GA1963@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>