x86/Kconfig/cpus: Fix/complete CPU type help texts

Move the generic help text explaining each CPU type and what to
select under the "Processor Family" prompt and not under the
M486 option. Also, amend it with the missing options.

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
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/1445244077-25120-1-git-send-email-bp@alien8.de


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