x86/compat: Separate ia32 and x32 compat ABIs

The x32 ABI is now independent of the ia32 compat ABI.  Common
code is now conditional on CONFIG_COMPAT, but unshared code like
syscall entry, signal handling, and the VDSO are under separate
config options.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1434974121-32575-13-git-send-email-brgerst@gmail.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>