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/pcm051_rev3_defconfig b/configs/pcm051_rev3_defconfig
index f449f58..a7b8775 100644
--- a/configs/pcm051_rev3_defconfig
+++ b/configs/pcm051_rev3_defconfig
@@ -1,5 +1,6 @@
 CONFIG_ARM=y
 CONFIG_TARGET_PCM051=y
+CONFIG_SPL_GPIO_SUPPORT=y
 CONFIG_SPL_EXT_SUPPORT=y
 CONFIG_SPL_FAT_SUPPORT=y
 CONFIG_SPL_ENV_SUPPORT=y