mmc: tmio: sdhi: Touch SCC only when UHS capable

Add check to avoid touching the SCC tuning registers in case the IP
doesn't support them or if the support isn't in place yet.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>