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/brxre1_defconfig b/configs/brxre1_defconfig
index d7b1765..29156f0 100644
--- a/configs/brxre1_defconfig
+++ b/configs/brxre1_defconfig
@@ -70,6 +70,8 @@
 CONFIG_SYS_REDUNDAND_ENVIRONMENT=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_BOOTP_SEND_HOSTNAME=y
+CONFIG_SYS_MMC_ENV_DEV=1
+CONFIG_SYS_MMC_ENV_PART=2
 CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_NETCONSOLE=y
 CONFIG_DM=y