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/T1040D4RDB_SPIFLASH_defconfig b/configs/T1040D4RDB_SPIFLASH_defconfig
index 77f8cfd..2ce9431 100644
--- a/configs/T1040D4RDB_SPIFLASH_defconfig
+++ b/configs/T1040D4RDB_SPIFLASH_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