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/smegw01_defconfig b/configs/smegw01_defconfig
index 2288c58..829cb4a 100644
--- a/configs/smegw01_defconfig
+++ b/configs/smegw01_defconfig
@@ -17,6 +17,8 @@
 CONFIG_IMX_HAB=y
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="if run loadimage; then run mmcboot; fi; "
 CONFIG_HUSH_PARSER=y
 # CONFIG_CMD_BOOTD is not set
 CONFIG_CMD_BOOTZ=y