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/pxm2_defconfig b/configs/pxm2_defconfig
index b88b7c9..6a12cce 100644
--- a/configs/pxm2_defconfig
+++ b/configs/pxm2_defconfig
@@ -77,6 +77,7 @@
 CONFIG_SYS_DFU_DATA_BUF_SIZE=0x100000
 CONFIG_SYS_I2C_LEGACY=y
 CONFIG_SPL_SYS_I2C_LEGACY=y
+CONFIG_SYS_I2C_SPEED=400000
 # CONFIG_SPL_DM_MMC is not set
 CONFIG_MMC_OMAP_HS=y
 CONFIG_MTD=y