Convert CONFIG_SPL_LIBGENERIC_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/ot1200_spl_defconfig b/configs/ot1200_spl_defconfig
index 3b5752f..814b554 100644
--- a/configs/ot1200_spl_defconfig
+++ b/configs/ot1200_spl_defconfig
@@ -2,6 +2,7 @@
 CONFIG_ARCH_MX6=y
 CONFIG_SPL_GPIO_SUPPORT=y
 CONFIG_SPL_LIBCOMMON_SUPPORT=y
+CONFIG_SPL_LIBGENERIC_SUPPORT=y
 CONFIG_TARGET_OT1200=y
 CONFIG_SPL_I2C_SUPPORT=y
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=arch/arm/imx-common/spl_sd.cfg,MX6Q"