mmc: tmio: add actual clock support as option

Some controller is supporting actual clock on SD_CLK_CTRL :: DIV[7:0].
Renesas SH-Mobile SDHI doesn't support,
but, Renesas R-Car SDHI supports it.
This patch adds new TMIO_MMC_CLK_ACTUAL flag for it.

[Kuninori Morimoto: tidyuped for upstreaming]

Tested-by: Nguyen Xuan Nui <nx-nui@jinso.co.jp>
Tested-by: Hiep Cao Minh <cm-hiep@jinso.co.jp>
Signed-off-by: Shinobu Uehara <shinobu.uehara.xc@renesas.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>