powerpc: Align p_toc

p_toc is an 8 byte relative offset to the TOC that we place in the
text section. This means it is only 4 byte aligned where it should
be 8 byte aligned. Add an explicit alignment.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>