Convert CONFIG_USE_BOOTCOMMAND et al to Kconfig

This converts the following to Kconfig:
   CONFIG_USE_BOOTCOMMAND
   CONFIG_BOOTCOMMAND
   CONFIG_RAMBOOTCOMMAND
   CONFIG_NFSBOOTCOMMAND

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/mx7ulp_evk_plugin_defconfig b/configs/mx7ulp_evk_plugin_defconfig
index 141592f..0f8e9e8 100644
--- a/configs/mx7ulp_evk_plugin_defconfig
+++ b/configs/mx7ulp_evk_plugin_defconfig
@@ -11,6 +11,8 @@
 CONFIG_DEFAULT_DEVICE_TREE="imx7ulp-evk"
 CONFIG_TARGET_MX7ULP_EVK=y
 CONFIG_SYS_LOAD_ADDR=0x60800000
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="mmc dev ${mmcdev}; if mmc rescan; then if run loadbootscript; then run bootscript; else if run loadimage; then run mmcboot; fi; fi; fi"
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_MEMTEST=y