mmc: sdhci: add platform get_max_timeout_count hook

Currently the max timeout count is hardcode to 1 << 27 for calcuate
the max_busy_timeout, however, for some platforms the max timeout
count may not be 1 << 27, e.g. i.MX uSDHC is 1 << 28.
Thus 1 << 27 is not correct for such platform.

It is also possible that other platforms may have different values.
To be flexible, we add a get_max_timeout_count hook to get the correct
maximum timeout value for these platforms.

Reviewed-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Dong Aisheng <b29396@freescale.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
index 4a5cd5e..b130509 100644
--- a/drivers/mmc/host/sdhci.h
+++ b/drivers/mmc/host/sdhci.h
@@ -281,6 +281,7 @@
 	unsigned int	(*get_max_clock)(struct sdhci_host *host);
 	unsigned int	(*get_min_clock)(struct sdhci_host *host);
 	unsigned int	(*get_timeout_clock)(struct sdhci_host *host);
+	unsigned int	(*get_max_timeout_count)(struct sdhci_host *host);
 	void		(*set_bus_width)(struct sdhci_host *host, int width);
 	void (*platform_send_init_74_clocks)(struct sdhci_host *host,
 					     u8 power_mode);