x86/microcode/intel: Unexport save_mc_for_early()

It is used only in intel.c, drop the CONFIG_HOTPLUG_CPU ifdeffery from
the header and turn it into a void function because its return value
wasn't being used anyway.

No functionality change.

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/1465225850-7352-8-git-send-email-bp@alien8.de


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