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>

arch/powerpc/kernel/head_64.S

@@ -703,6 +703,7 @@ _GLOBAL(relative_toc)
 	mtlr	r0
 	blr
 
+.balign 8
 p_toc:	.llong	__toc_start + 0x8000 - 0b
 
 /*