mmc: host: sh_mobile_sdhi: don't populate unneeded functions

Populating card_busy caused a side-effect on a chip variant we don't
have documentation for (r8a73a4). So, enable it and voltage switching
only on devices known to support those features.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Fixes: 452e5eef ("mmc: tmio: Add UHS-I mode support")