Convert CONFIG_SYS_I2C_SPEED et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_I2C_SPEED
   CONFIG_SYS_I2C_SLAVE

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/icnova-a20-swac_defconfig b/configs/icnova-a20-swac_defconfig
index 84fe310c..de45560 100644
--- a/configs/icnova-a20-swac_defconfig
+++ b/configs/icnova-a20-swac_defconfig
@@ -16,6 +16,8 @@
 CONFIG_SPL_I2C=y
 CONFIG_CMD_UNZIP=y
 CONFIG_SYS_I2C_MVTWSI=y
+CONFIG_SYS_I2C_SLAVE=0x7f
+CONFIG_SYS_I2C_SPEED=400000
 CONFIG_PHY_REALTEK=y
 CONFIG_ETH_DESIGNWARE=y
 CONFIG_MII=y