powerpc: Move setup_board_extra() into a PPC file

We don't need this PPC-specific function in generic code. Move it to
the powerpc directory.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
index 3c97476..4f68613 100644
--- a/arch/powerpc/lib/Makefile
+++ b/arch/powerpc/lib/Makefile
@@ -17,6 +17,7 @@
 endif
 endif
 
+obj-$(CONFIG_SYS_EXTBDINFO) += setup.o
 ifdef MINIMAL
 obj-y += cache.o time.o
 obj-y += ticks.o