percpu: include/asm-generic/percpu.h should contain only arch-overridable parts

The roles of the various percpu header files has become unclear.
There are four header files involved.

 include/linux/percpu-defs.h
 include/linux/percpu.h
 include/asm-generic/percpu.h
 arch/*/include/asm/percpu.h

The original intention for include/asm-generic/percpu.h is providing
generic definitions for arch-overridable parts; however, it now hosts
various stuff which can't be overridden by archs.

Also, include/linux/percpu-defs.h was initially added to contain
section and percpu variable definition macros so that arch header
files can make use of them without worrying about introducing cyclic
inclusion dependency by including include/linux/percpu.h; however,
arch headers sometimes need to access percpu variables too and this is
one of the reasons why some accessors were implemented in
include/linux/asm-generic/percpu.h.

Let's clear up the situation by making include/asm-generic/percpu.h
contain only arch-overridable parts and moving accessors and
operations into include/linux/percpu-defs.  Note that this patch only
moves things from include/asm-generic/percpu.h.
include/linux/percpu.h will be taken care of by later patches.

This patch moves the followings.

* SHIFT_PERCPU_PTR() / VERIFY_PERCPU_PTR()
* per_cpu()
* raw_cpu_ptr()
* this_cpu_ptr()
* __get_cpu_var()
* __raw_get_cpu_var()
* __this_cpu_ptr()
* PER_CPU_[SHARED_]ALIGNED_SECTION
* PER_CPU_[SHARED_]ALIGNED_SECTION
* PER_CPU_FIRST_SECTION

This patch is pure reorganization.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Christoph Lameter <cl@linux.com>