evb-rk3128: Migrate CONFIG_ENV_IS_IN_MMC to defconfig

This board is setting CONFIG_ENV_IS_IN_MMC in the header rather than
defconfig, fix.

Cc: Kever Yang <kever.yang@rock-chips.com>
Signed-off-by: Tom Rini <trini@konsulko.com>

configs/evb-rk3128_defconfig

@@ -17,6 +17,7 @@ CONFIG_CMD_USB_MASS_STORAGE=y
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_TIME=y
 CONFIG_DEFAULT_DEVICE_TREE="rk3128-evb"
+CONFIG_ENV_IS_IN_MMC=y
 CONFIG_REGMAP=y
 CONFIG_SYSCON=y
 CONFIG_CLK=y

include/configs/evb_rk3128.h

@@ -8,7 +8,6 @@
 
 #include <configs/rk3128_common.h>
 
-#define CONFIG_ENV_IS_IN_MMC
 #define CONFIG_SYS_MMC_ENV_DEV 0
 
 #endif