Convert CONFIG_SPL_LIBCOMMON_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/x600_defconfig b/configs/x600_defconfig
index cae29a1..b055434 100644
--- a/configs/x600_defconfig
+++ b/configs/x600_defconfig
@@ -1,5 +1,6 @@
 CONFIG_ARM=y
 CONFIG_TARGET_X600=y
+CONFIG_SPL_LIBCOMMON_SUPPORT=y
 CONFIG_BOOTDELAY=3
 CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y