Convert CONFIG_ENV_MIN_ENTRIES et al to Kconfig

This converts the following to Kconfig:
   CONFIG_ENV_MIN_ENTRIES
   CONFIG_ENV_MAX_ENTRIES

Cc: Michal Simek <michal.simek@amd.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/helios4_defconfig b/configs/helios4_defconfig
index 2a1db65..4642eb1 100644
--- a/configs/helios4_defconfig
+++ b/configs/helios4_defconfig
@@ -51,6 +51,7 @@
 CONFIG_CMD_MVEBU_BUBT=y
 # CONFIG_SPL_PARTITION_UUIDS is not set
 CONFIG_ENV_OVERWRITE=y
+CONFIG_ENV_MIN_ENTRIES=128
 CONFIG_ARP_TIMEOUT=200
 CONFIG_NET_RETRY_COUNT=50
 CONFIG_NET_RANDOM_ETHADDR=y