ARM: 6515/1: Add zboot support for SuperH Mobile ARM

ARM: 6515/1: Add zboot support for SuperH Mobile ARM

When CONFIG_ZBOOT_ROM is selected, the resulting zImage file will be small
boot loader and may be burned to rom or flash.

This is the non-board-specific framework portion of this patch-set.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms@verge.net.au>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>