mmc: tmio: add tmio_mmc_host_alloc/free()

Current tmio_mmc driver is using tmio_mmc_data for driver/platform
specific data/callback, and it is needed for tmio_mmc_host_probe()
function. Because of this style, include/linux/mfd/tmio.h header has
tmio driver/framework specific data which is not needed from platform.

This patch adds new tmio_mmc_host_alloc/free() as cleanup preparation.
tmio driver specific data/callback will be implemented in tmio_mmc_host,
and platform specific data/callback will be implemented in tmio_mmc_data
in this cleanup.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>