powerpc/book64s: Move a few exception common handlers to make room

This moves the CBE RAS and facility unavailable "common" handlers
down to after the FWNMI page.

This frees up some space in the very demanded spaces before the
relocation-on vectors and before the FWNMI page. They are still
within 64K of __start, so CONFIG_RELOCATABLE should still work.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>