powerpc: Cleanup linker script using new linker script macros.

Signed-off-by: Tim Abbott <tabbott@ksplice.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: linuxppc-dev@ozlabs.org
Cc: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>