kconfig: Convert CONFIG_MXS_GPIO to Kconfig

This converts the following to Kconfig:
   CONFIG_MXS_GPIO

Travis-CI: https://travis-ci.org/lmajewski/u-boot-dfu/builds/571260789

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Acked-by: Peng Fan <peng.fan@nxp.com>
Acked-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/configs/mx23_olinuxino_defconfig b/configs/mx23_olinuxino_defconfig
index 3e4b7ab..fd045ad 100644
--- a/configs/mx23_olinuxino_defconfig
+++ b/configs/mx23_olinuxino_defconfig
@@ -26,6 +26,7 @@
 CONFIG_CMD_EXT2=y
 CONFIG_CMD_FAT=y
 CONFIG_ENV_IS_IN_MMC=y
+CONFIG_MXS_GPIO=y
 CONFIG_LED_STATUS=y
 CONFIG_LED_STATUS_GPIO=y
 CONFIG_LED_STATUS0=y