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/dserve_dsrv9703c_defconfig b/configs/dserve_dsrv9703c_defconfig
index 75f1ec8..60910c3 100644
--- a/configs/dserve_dsrv9703c_defconfig
+++ b/configs/dserve_dsrv9703c_defconfig
@@ -16,4 +16,6 @@
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
 CONFIG_SPL_I2C=y
 CONFIG_SYS_I2C_MVTWSI=y
+CONFIG_SYS_I2C_SLAVE=0x7f
+CONFIG_SYS_I2C_SPEED=400000
 CONFIG_USB_MUSB_HOST=y