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/mx6slevk_spl_defconfig b/configs/mx6slevk_spl_defconfig
index ca1042b..cf5b24e 100644
--- a/configs/mx6slevk_spl_defconfig
+++ b/configs/mx6slevk_spl_defconfig
@@ -9,6 +9,9 @@
 CONFIG_ENV_OFFSET=0x80000
 CONFIG_MX6SL=y
 CONFIG_TARGET_MX6SLEVK=y
+CONFIG_SYS_I2C_MXC_I2C1=y
+CONFIG_SYS_I2C_MXC_I2C2=y
+CONFIG_SYS_I2C_MXC_I2C3=y
 CONFIG_DM_GPIO=y
 CONFIG_DEFAULT_DEVICE_TREE="imx6sl-evk"
 CONFIG_SPL_TEXT_BASE=0x00908000
@@ -48,6 +51,7 @@
 CONFIG_BOUNCE_BUFFER=y
 CONFIG_DM_I2C=y
 CONFIG_SPL_SYS_I2C_LEGACY=y
+CONFIG_SYS_I2C_MXC=y
 CONFIG_FSL_USDHC=y
 CONFIG_MTD=y
 CONFIG_DM_SPI_FLASH=y