Blackfin: rewrite resync_core_{i,d}cache() SMP logic to avoid per_cpu data

This functions are implicitly called by core functions like cpu_relax(),
and since those functions may be called early on before common code has
initialized the per-cpu data area, we need to tweak the stats gathering.
Now the statistics are maintained in common bss which makes these funcs
safe to use as soon as the C runtime env is setup.

Signed-off-by: Graf Yang <graf.yang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>