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/T1042RDB_PI_NAND_SECURE_BOOT_defconfig b/configs/T1042RDB_PI_NAND_SECURE_BOOT_defconfig
index addfe2b..e20f513 100644
--- a/configs/T1042RDB_PI_NAND_SECURE_BOOT_defconfig
+++ b/configs/T1042RDB_PI_NAND_SECURE_BOOT_defconfig
@@ -1,4 +1,5 @@
 CONFIG_PPC=y
+CONFIG_SPL_I2C_SUPPORT=y
 CONFIG_SPL_ENV_SUPPORT=y
 CONFIG_MPC85xx=y
 CONFIG_TARGET_T104XRDB=y