mmc: sdhi: Add write16_hook

Some controllers require waiting for the bus to become idle
before writing to some registers. I have implemented this
by adding a hook to sd_ctrl_write16() and implementing
a hook for SDHI which waits for the bus to become idle.

Cc: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Cc: Magnus Damm <magnus.damm@gmail.com>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/host/tmio_mmc.h

@@ -153,6 +153,11 @@ static inline u32 sd_ctrl_read32(struct tmio_mmc_host *host, int addr)
 
 static inline void sd_ctrl_write16(struct tmio_mmc_host *host, int addr, u16 val)
 {
+	/* If there is a hook and it returns non-zero then there
+	 * is an error and the write should be skipped
+	 */
+	if (host->pdata->write16_hook && host->pdata->write16_hook(host, addr))
+		return;
 	writew(val, host->ctl + (addr << host->bus_shift));
 }