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/rock64-rk3328_defconfig b/configs/rock64-rk3328_defconfig
index a7f8823..e6922e2 100644
--- a/configs/rock64-rk3328_defconfig
+++ b/configs/rock64-rk3328_defconfig
@@ -43,6 +43,7 @@
 CONFIG_TPL_OF_PLATDATA=y
 CONFIG_ENV_IS_IN_MMC=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_SYS_MMC_ENV_DEV=1
 CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_TPL_DM=y
 CONFIG_REGMAP=y