mmc: mxs-mmc: move header from mach into linux folder

Rename arch/arm/mach-mxs/include/mach/mmc.h to
include/linux/mmc/mxs-mmc.h, so that mxs-mmc driver becomes
<mach/*> inclusion free.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Marek Vasut <marex@denx.de>
Acked-by: Chris Ball <cjb@laptop.org>