sh: romImage support V2

This patch contains support for the romImage build target V2.

The resulting romImage file should be burned to rom
or flash and could be used as small boot loader.

Board code should keep their setup code in the file
romimage.h located in their mach include directory.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>