Convert CONFIG_SYS_I2C_MXC et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_I2C_MXC
   CONFIG_SYS_I2C_MXC_I2C1
   CONFIG_SYS_I2C_MXC_I2C2
   CONFIG_SYS_I2C_MXC_I2C3
   CONFIG_SYS_I2C_MXC_I2C4

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/mx6sllevk_plugin_defconfig b/configs/mx6sllevk_plugin_defconfig
index 6fc4915..c29121d 100644
--- a/configs/mx6sllevk_plugin_defconfig
+++ b/configs/mx6sllevk_plugin_defconfig
@@ -37,6 +37,7 @@
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_BOUNCE_BUFFER=y
 CONFIG_DM_I2C=y
+CONFIG_SYS_I2C_MXC=y
 CONFIG_FSL_USDHC=y
 CONFIG_MTD=y
 CONFIG_PINCTRL=y