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/Cubieboard_defconfig b/configs/Cubieboard_defconfig
index 427dc11..93a7932 100644
--- a/configs/Cubieboard_defconfig
+++ b/configs/Cubieboard_defconfig
@@ -11,6 +11,8 @@
 CONFIG_SPL_I2C=y
 CONFIG_SCSI_AHCI=y
 CONFIG_SYS_I2C_MVTWSI=y
+CONFIG_SYS_I2C_SLAVE=0x7f
+CONFIG_SYS_I2C_SPEED=400000
 CONFIG_MII=y
 CONFIG_SUN4I_EMAC=y
 CONFIG_SCSI=y