mmc: tmio: move MFD variant reset to a platform hook

mmc: tmio: move MFD variant reset to a platform hook

CTL_RESET_SDIO register is specific to the TMIO MFD (tmio_mmc.c).

Add a new hook host->reset() for performing a platform-specific
reset sequence, and move CTL_RESET_SDIO over there.

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