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/m53evk_defconfig b/configs/m53evk_defconfig
index 0bd39e2..145b44d 100644
--- a/configs/m53evk_defconfig
+++ b/configs/m53evk_defconfig
@@ -1,5 +1,6 @@
 CONFIG_ARM=y
 CONFIG_TARGET_M53EVK=y
+CONFIG_SPL_GPIO_SUPPORT=y
 CONFIG_FIT=y
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/denx/m53evk/imximage.cfg"
 CONFIG_BOOTDELAY=3