Convert CONFIG_SPL_I2C_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 d8cf7d9..ddedfd6 100644
--- a/configs/k2g_evm_defconfig
+++ b/configs/k2g_evm_defconfig
@@ -1,6 +1,7 @@
 CONFIG_ARM=y
 CONFIG_ARCH_KEYSTONE=y
 CONFIG_TARGET_K2G_EVM=y
+CONFIG_SPL_I2C_SUPPORT=y
 CONFIG_DEFAULT_DEVICE_TREE="k2g-evm"
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_VERSION_VARIABLE=y