mmc: Removed the unused public mmc boot.h header

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/mmc/boot.h

-#ifndef LINUX_MMC_BOOT_H
-#define LINUX_MMC_BOOT_H
-
-enum { MMC_PROGRESS_ENTER, MMC_PROGRESS_INIT,
-       MMC_PROGRESS_LOAD, MMC_PROGRESS_DONE };
-
-#endif /* LINUX_MMC_BOOT_H */