mmc: sh_mmcif: move platform_data header to proper location

We have a dedicated directory for platform_data meanwhile, don't spoil
the MMC directory with it.

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/20220412093102.3428-1-wsa+renesas@sang-engineering.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>