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/smartweb_defconfig b/configs/smartweb_defconfig
index af6e925..0e99c36 100644
--- a/configs/smartweb_defconfig
+++ b/configs/smartweb_defconfig
@@ -27,6 +27,8 @@
 CONFIG_AUTOBOOT_KEYED=y
 CONFIG_AUTOBOOT_PROMPT="Autobooting in %d seconds, press \"<Esc><Esc>\" to stop\n"
 CONFIG_AUTOBOOT_STOP_STR="\x1b\x1b"
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="run flashboot"
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SPL_NAND_SUPPORT=y