mmc: sdhci: convert reset into a library function

Rather than having platform_reset_enter/platform_reset_exit methods,
turn the core of the reset handling into a library function which
platforms can call at the appropriate moment in their (new) reset
method.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Tested-by: Markus Pargmann <mpa@pengutronix.de>
Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <chris@printf.net>

drivers/mmc/host/sdhci-pltfm.c

@@ -46,6 +46,7 @@ EXPORT_SYMBOL_GPL(sdhci_pltfm_clk_get_max_clock);
 
 static const struct sdhci_ops sdhci_pltfm_ops = {
 	.set_bus_width = sdhci_set_bus_width,
+	.reset = sdhci_reset,
 };
 
 #ifdef CONFIG_OF