ACPI: processor: mv processor_core.c processor_driver.c

The ACPI processor driver can be built as a module. But it has
pieces of code that should always be built statically into the
kernel.

The plan is for processor_core.c to contain the static bits while
processor_driver.c contains the module-like bits.

Since the bulk of the code in the current processor_core.c is
module-like, first step is to rename the file to processor_driver.c

Next step will re-create processor_core.c and cherry-pick out
the static bits.

Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>