mmc: tmio, renesas_sdhi: move struct tmio_mmc_dma to renesas_sdhi.h

struct tmio_mmc_dma looks like TMIO core data, but in fact, Renesas
private data.  Move it to renesas_sdhi.h (probably, it is better to
rename it to renesas_sdhi_dma, or squash it into struct renesas_sdhi).

I also moved struct renesas_sdhi and host_to_priv() to that header
because they are necessary to convert the tmio_mmc_host pointer into
the renesas_sdhi pointer.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>