x86/kconfig: Clean up 32-bit compat options

Introduce a 'COMPAT_32' helper config value for 'X86_32 || IA32_EMULATION'
and use it.

Also move some selects to this new option, to remove more selects from
the generic X86 section.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>