mmc: core: First step in cleaning up private mmc header files

This is the first step in cleaning up the private mmc header files. In this
change we makes sure each header file builds standalone, as that helps to
resolve dependencies.

While changing this, it also seems reasonable to stop including other
headers from inside a header itself which it don't depend upon.
Additionally, in some cases such dependencies are better resolved by
forward declaring the needed struct.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>

drivers/mmc/core/block.h

@@ -1 +1,9 @@
+#ifndef _MMC_CORE_BLOCK_H
+#define _MMC_CORE_BLOCK_H
+
+struct mmc_queue;
+struct request;
+
 int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req);
+
+#endif