ARM: shmobile: marzen: Include mmc/host.h

mmc/host.h provides MMC_CAP_SD_HIGHSPEED which is used in board-marzen.c

This resolves a build problem observed when compiling with
"mmc: tmio: remove unused and deprecated symbols" applied.

Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>