powerpc: Make slb_shadow a local

The only external user of slb_shadow is the pseries lpar code, and it
can access through the paca array instead.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --cc arch/powerpc/include/asm/lppaca.h
Simple merge

diff --cc arch/powerpc/kernel/paca.c
Simple merge

diff --cc arch/powerpc/platforms/pseries/lpar.c
Simple merge