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/ls2080aqds_nand_defconfig b/configs/ls2080aqds_nand_defconfig
index 1fa0589..ffbf6a9 100644
--- a/configs/ls2080aqds_nand_defconfig
+++ b/configs/ls2080aqds_nand_defconfig
@@ -1,5 +1,6 @@
 CONFIG_ARM=y
 CONFIG_TARGET_LS2080AQDS=y
+CONFIG_SPL_I2C_SUPPORT=y
 CONFIG_SPL_ENV_SUPPORT=y
 CONFIG_SPL_DRIVERS_MISC_SUPPORT=y
 CONFIG_DEFAULT_DEVICE_TREE="fsl-ls2080a-qds"