mmc: sh_mmcif: Remove unused clk_ctrl2_present from the platform data

There are currently no users of the clk_ctrl2_present member from the
platform data, so let's remove it.

Note, as some of the sh_mmcif variants may support clk_ctrl2, let's keep
the current code in the driver, which deals with this. For future support,
we should invent a DT binding instead, but let's leave that until it's
needed.

Cc: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>