x86: add X86_32 dependency to i386 specific symbols in Kconfig.i386

To ease unification of Kconfig.i386 and Kconfig.x86_64
add X86_32 dependencies to all i386 specific symbols.

This patch introduce no functional changes but is one step
towards unification. This smaller step is used to ease
review of the patch set.

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>