s390: switch to dynamic percpu allocator

s390: switch to dynamic percpu allocator

64bit s390 shares the same problem with alpha regarding percpu symbol
addressing from modules.  It needs assembly magic to force GOTENT
reference when building module as the percpu address will be outside
the usual 4G range from the module text.  This can be solved by using
weak percpu variable definitions.

This patch makes s390 use weak definitions and switch to dynamic
percpu allocator.  Please note that weak attribute is not added if
!SMP as percpu variables behave exactly the same as normal variables
on UP.

Compile tested.  Generation of GOTENT reference verified.

This patch is based on Ivan Kokshaysky's alpha percpu patch.

[ Impact: use dynamic percpu allocator ]

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>