mmc: slot-gpio: Make mmc_gpio_alloc() available for MMC core

As a step in moving slot-gpio functions/structs closer to the MMC core,
let's add a local header file for slot-gpio.

In this initial step we move mmc_gpio_alloc() into the header file,
to make it available for the MMC core. Following patches will show the
utilization of it.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
diff --git a/drivers/mmc/core/slot-gpio.c b/drivers/mmc/core/slot-gpio.c
index f9a0c6e..ec918c2 100644
--- a/drivers/mmc/core/slot-gpio.c
+++ b/drivers/mmc/core/slot-gpio.c
@@ -18,6 +18,8 @@
 #include <linux/module.h>
 #include <linux/slab.h>
 
+#include "slot-gpio.h"
+
 struct mmc_gpio {
 	struct gpio_desc *ro_gpio;
 	struct gpio_desc *cd_gpio;
@@ -38,7 +40,7 @@
 	return IRQ_HANDLED;
 }
 
-static int mmc_gpio_alloc(struct mmc_host *host)
+int mmc_gpio_alloc(struct mmc_host *host)
 {
 	size_t len = strlen(dev_name(host->parent)) + 4;
 	struct mmc_gpio *ctx;