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/work_92105_defconfig b/configs/work_92105_defconfig
index bfb3cd0..7fc43f3 100644
--- a/configs/work_92105_defconfig
+++ b/configs/work_92105_defconfig
@@ -46,6 +46,7 @@
 CONFIG_SYS_I2C_LEGACY=y
 CONFIG_SPL_SYS_I2C_LEGACY=y
 CONFIG_SYS_I2C_LPC32XX=y
+CONFIG_SYS_I2C_SPEED=350000
 CONFIG_SYS_I2C_EEPROM_ADDR=0x56
 # CONFIG_MMC is not set
 CONFIG_MTD=y