x86: Export 'boot_cpu_physical_apicid' to modules

Commit 9ebddac7 "ACPI, x86: Fix extended error log driver to depend on
CONFIG_X86_LOCAL_APIC" fixed a build error when CONFIG_X86_LOCAL_APIC was not
selected and !CONFIG_SMP.

However, since CONFIG_ACPI_EXTLOG is tristate, there is a second build error:

  ERROR: "boot_cpu_physical_apicid" [drivers/acpi/acpi_extlog.ko] undefined!

The symbol needs to be exported for it to be available.

Signed-off-by: David Rientjes <rientjes@google.com>
Acked-by: Tony Luck <tony.luck@intel.com>
Cc: Chen Gong <gong.chen@linux.intel.com>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Link: http://lkml.kernel.org/r/alpine.DEB.2.02.1311141504080.30112@chino.kir.corp.google.com


[ Changed it to a _GPL() export. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>