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/MSI_Primo73_defconfig b/configs/MSI_Primo73_defconfig
index 5559444..87fd3b9 100644
--- a/configs/MSI_Primo73_defconfig
+++ b/configs/MSI_Primo73_defconfig
@@ -1,5 +1,6 @@
 CONFIG_ARM=y
 CONFIG_ARCH_SUNXI=y
+CONFIG_SPL_I2C_SUPPORT=y
 CONFIG_MACH_SUN7I=y
 CONFIG_DRAM_CLK=384
 CONFIG_VIDEO_LCD_MODE="x:1024,y:600,depth:18,pclk_khz:60000,le:60,ri:160,up:13,lo:12,hs:100,vs:10,sync:3,vmode:0"