sh: add romImage MMCIF boot for sh7724 and Ecovec V2

This patch is V2 of the MMCIF romImage boot support
for sh7724 and the Ecovec board. With this patch
applied and CONFIG_ROMIMAGE_MMCIF selected the
romImage kernel image can be written to a MMC card
and booted directly by the sh7724 cpu.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>