powerpc: Fix lwsync feature fixup vs. modules on 64-bit

Anton's commit enabling the use of the lwsync fixup mechanism on 64-bit
breaks modules. The lwsync fixup section uses .long instead of the
FTR_ENTRY_OFFSET macro used by other fixups sections, and thus will
generate 32-bit relocations that our module loader cannot resolve.

This changes it to use the same type as other feature sections.

Note however that we might want to consider using 32-bit for all the
feature fixup offsets and add support for R_PPC_REL32 to module_64.c
instead as that would reduce the size of the kernel image. I'll leave
that as an exercise for the reader for now...

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>