mmc: sdhci-pxa: move platform data to include/linux/platform_data

As suggested by Arnd, move platform data to include/linux/platform_data
in order to improve build coverage for the driver.

Signed-off-by: Zhangfei Gao <zhangfei.gao@marvell.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Chris Ball <cjb@laptop.org>