Add DT support for SDHI0, SDHI1 and SDHI2 on Koelsch.

The board specific handling of CD and WP pins are
using GPIOs. SDHI0 and SDHI1 are hooked up to regular
SD connectors while SDHI2 is using micro-SD which
is lacking WP signal.
Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>