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/k2g_evm_defconfig b/configs/k2g_evm_defconfig
index ddedfd6..722e2aa 100644
--- a/configs/k2g_evm_defconfig
+++ b/configs/k2g_evm_defconfig
@@ -1,5 +1,6 @@
 CONFIG_ARM=y
 CONFIG_ARCH_KEYSTONE=y
+CONFIG_SPL_LIBCOMMON_SUPPORT=y
 CONFIG_TARGET_K2G_EVM=y
 CONFIG_SPL_I2C_SUPPORT=y
 CONFIG_DEFAULT_DEVICE_TREE="k2g-evm"