Convert CONFIG_CMD_ENV_FLAGS to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_ENV_FLAGS

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/ids8313_defconfig b/configs/ids8313_defconfig
index 165e2eb..2accd31 100644
--- a/configs/ids8313_defconfig
+++ b/configs/ids8313_defconfig
@@ -13,6 +13,7 @@
 CONFIG_AUTOBOOT_KEYED=y
 CONFIG_AUTOBOOT_PROMPT="Enter password - autoboot in %d seconds...\n"
 CONFIG_AUTOBOOT_DELAY_STR="ids"
+CONFIG_CMD_ENV_FLAGS=y
 CONFIG_CMD_SPI=y
 CONFIG_CMD_I2C=y
 # CONFIG_CMD_SETEXPR is not set
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index 410277a..9e46fa6 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -23,6 +23,7 @@
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_GREPENV=y
 CONFIG_CMD_ENV_CALLBACK=y
+CONFIG_CMD_ENV_FLAGS=y
 CONFIG_CMD_MD5SUM=y
 CONFIG_LOOPW=y
 CONFIG_CMD_MEMTEST=y
diff --git a/configs/sandbox_noblk_defconfig b/configs/sandbox_noblk_defconfig
index 090e057..4bf1f4b 100644
--- a/configs/sandbox_noblk_defconfig
+++ b/configs/sandbox_noblk_defconfig
@@ -23,6 +23,7 @@
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_GREPENV=y
 CONFIG_CMD_ENV_CALLBACK=y
+CONFIG_CMD_ENV_FLAGS=y
 CONFIG_CMD_MD5SUM=y
 CONFIG_LOOPW=y
 CONFIG_CMD_MEMTEST=y
diff --git a/configs/sandbox_spl_defconfig b/configs/sandbox_spl_defconfig
index b623e29..cbe4185 100644
--- a/configs/sandbox_spl_defconfig
+++ b/configs/sandbox_spl_defconfig
@@ -31,6 +31,7 @@
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_GREPENV=y
 CONFIG_CMD_ENV_CALLBACK=y
+CONFIG_CMD_ENV_FLAGS=y
 CONFIG_CMD_MD5SUM=y
 CONFIG_LOOPW=y
 CONFIG_CMD_MEMTEST=y