mmc: dw_mmc: check fifo status with a timeout in fifo mode

While trying to enable the dw_mmc on rk3188 I managed to confuse
and hang the dw_mmc controller into not delivering further data.
The fifo state never became ready and the driver was iterating in
the while loop reading 0-byte packets forever.

So inspired by how other implementations handle this, check the fifo-
state beforhand and add a timeout to catch any glaring fifo issues
without hanging uboot altogether.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>

include/dwmmc.h

@@ -103,6 +103,8 @@
 #define DWMCI_CTYPE_8BIT	(1 << 16)
 
 /* Status Register */
+#define DWMCI_FIFO_EMPTY	(1 << 2)
+#define DWMCI_FIFO_FULL		(1 << 3)
 #define DWMCI_BUSY		(1 << 9)
 #define DWMCI_FIFO_MASK		0x1fff
 #define DWMCI_FIFO_SHIFT	17