x86: start unification of arch/x86/Kconfig.*

This step introduces the file arch/x86/Kconfig
which contains all the menu's from "Power Management"
and below.

The main part of the new Kconfig file is shared
and the remaining i386/x86_64 specific symbols
are covered by dependencies.

A x86_64 allmodconfig build did not show any differences.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>