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/phycore-rk3288_defconfig b/configs/phycore-rk3288_defconfig
index 9619aa6..a754d24 100644
--- a/configs/phycore-rk3288_defconfig
+++ b/configs/phycore-rk3288_defconfig
@@ -39,6 +39,7 @@
 CONFIG_OF_SPL_REMOVE_PROPS="pinctrl-0 pinctrl-names clock-names interrupt-parent assigned-clocks assigned-clock-rates assigned-clock-parents"
 CONFIG_ENV_IS_IN_MMC=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_SYS_MMC_ENV_DEV=1
 CONFIG_REGMAP=y
 CONFIG_SPL_REGMAP=y
 CONFIG_SYSCON=y