Convert CONFIG_SYS_MMC_ENV_DEV et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_MMC_ENV_DEV
   CONFIG_SYS_MMC_ENV_PART

Note that with this conversion we now have consistent behavior with
respect to ensuring that we have always selected the correct MMC
device and hardware partition.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/sei510_defconfig b/configs/sei510_defconfig
index b74c738..fc846fa 100644
--- a/configs/sei510_defconfig
+++ b/configs/sei510_defconfig
@@ -34,6 +34,8 @@
 CONFIG_OF_CONTROL=y
 CONFIG_ENV_IS_IN_MMC=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_SYS_MMC_ENV_DEV=2
+CONFIG_SYS_MMC_ENV_PART=1
 CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_USB_FUNCTION_FASTBOOT=y
 CONFIG_FASTBOOT_BUF_ADDR=0x6000000