ACPI processor: Fix section mismatch for processor_add()

Due to the merge of processor_start() (declared with __cpuinit) into
processor_add(), a section mismatch warning appears:

WARNING: drivers/built-in.o(.text+0x4d59d): Section mismatch in reference
from the function acpi_processor_add() to the function
.cpuinit.text:acpi_processor_power_init()
...

This patch fixes the warning by declaring processor_add() as __cpuinit
and also declares acpi_processor_add_fs() as __cpuinit as it is only
used in acpi_processor_add().

Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>