local_t : adding and standardising local atomic primitives

local_t : adding and standardising local atomic primitives

These patches extend and standardise local_t operations on each architectures,
allowing a rich set of atomic operations to be done on per-cpu data with
minimal performance impact. On architectures where there seems to be no
difference between the SMP and UP operation (same memory barriers, same
LOCKing), local.h simply includes asm-generic/local.h, which removes duplicated
code from the current kernel tree.

These patches apply on 2.6.20.
It depends on the patch "atomic.h : standardising atomic primitives"

These patches compile fine against :

arm
i686
ia64
m68k
mips
mipsel
x86_64
ppc 405
powerpc 970
s390
sparc
sparc64

Signed-off-by : Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>