mmc: mtk-sd: fix SPL compilation when GPIO=y and SPL_GPIO=n

It is not possible to link the SPL image when CONFIG_GPIO is enabled
but CONFIG_SPL_GPIO is not.  Use the IS_ENABLED macro instead to
correctly check whether CONFIG_{SPL_}GPIO is enabled.

This commit fixes the following errors:
	* undefined reference to `dm_gpio_get_value
	* undefined reference to `gpio_request_by_name'

Signed-off-by: Fabien Parent <fparent@baylibre.com>
[trini: Move guard to fix warning in msdc_ops_get_wp()]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/mmc/mtk-sd.c b/drivers/mmc/mtk-sd.c
index e668df7..d3f0778 100644
--- a/drivers/mmc/mtk-sd.c
+++ b/drivers/mmc/mtk-sd.c
@@ -269,7 +269,7 @@
 	bool builtin_cd;
 
 	/* card detection / write protection GPIOs */
-#ifdef CONFIG_DM_GPIO
+#if IS_ENABLED(DM_GPIO)
 	struct gpio_desc gpio_wp;
 	struct gpio_desc gpio_cd;
 #endif
@@ -849,7 +849,7 @@
 		return !(val & MSDC_PS_CDSTS);
 	}
 
-#ifdef CONFIG_DM_GPIO
+#if IS_ENABLED(DM_GPIO)
 	if (!host->gpio_cd.dev)
 		return 1;
 
@@ -861,9 +861,9 @@
 
 static int msdc_ops_get_wp(struct udevice *dev)
 {
+#if IS_ENABLED(DM_GPIO)
 	struct msdc_host *host = dev_get_priv(dev);
 
-#ifdef CONFIG_DM_GPIO
 	if (!host->gpio_wp.dev)
 		return 0;
 
@@ -1332,7 +1332,7 @@
 	if (ret < 0)
 		return ret;
 
-#ifdef CONFIG_DM_GPIO
+#if IS_ENABLED(DM_GPIO)
 	gpio_request_by_name(dev, "wp-gpios", 0, &host->gpio_wp, GPIOD_IS_IN);
 	gpio_request_by_name(dev, "cd-gpios", 0, &host->gpio_cd, GPIOD_IS_IN);
 #endif