Convert CONFIG_SPL_GPIO_SUPPORT to Kconfig

Move this option to Kconfig and tidy up existing uses.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/pcm058_defconfig b/configs/pcm058_defconfig
index 14913bb..61d2d28 100644
--- a/configs/pcm058_defconfig
+++ b/configs/pcm058_defconfig
@@ -1,5 +1,6 @@
 CONFIG_ARM=y
 CONFIG_ARCH_MX6=y
+CONFIG_SPL_GPIO_SUPPORT=y
 CONFIG_TARGET_PCM058=y
 CONFIG_SPL_EXT_SUPPORT=y
 CONFIG_FIT=y