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/birdland_bav335a_defconfig b/configs/birdland_bav335a_defconfig
index 9299637..dc0f63c 100644
--- a/configs/birdland_bav335a_defconfig
+++ b/configs/birdland_bav335a_defconfig
@@ -3,6 +3,7 @@
 CONFIG_SPL_GPIO_SUPPORT=y
 CONFIG_SPL_EXT_SUPPORT=y
 CONFIG_SPL_FAT_SUPPORT=y
+CONFIG_SPL_I2C_SUPPORT=y
 CONFIG_BAV_VERSION=1
 CONFIG_FIT=y
 CONFIG_SYS_EXTRA_OPTIONS="SERIAL1,CONS_INDEX=1"