[PATCH] Move variables in ppc64 head.S from .data to .bss

The ppc64 head.S defines several zero-initialized structures, such as
the empty_zero_page and the kernel top-level pagetable.  Currently
they are defined to be in the data section.  However, they're not used
until after the bss is cleared, so this patch moves them to the bss,
saving two and a half pages from the vmlinux.

Signed-off-by: David Gibson <dwg@au1.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>