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/warp7_defconfig b/configs/warp7_defconfig
index 19c0c18..b5d4f3d 100644
--- a/configs/warp7_defconfig
+++ b/configs/warp7_defconfig
@@ -43,6 +43,7 @@
 CONFIG_DFU_MMC=y
 CONFIG_SYS_DFU_DATA_BUF_SIZE=0x1000000
 CONFIG_DM_I2C=y
+CONFIG_SYS_I2C_MXC=y
 CONFIG_SUPPORT_EMMC_BOOT=y
 CONFIG_FSL_USDHC=y
 CONFIG_MTD=y