i2c: i2c-sh_mobile kconfig update for SH-Mobile ARM

Update the Kconfig entry for the i2c-sh_mobile driver to
enable build on SH-Mobile ARM platforms

Signed-off-by: Kuninori Morimoto <morimoto.kuninori@renesas.com>
Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>