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/deneb_defconfig b/configs/deneb_defconfig
index c51d6a3..6dfd336 100644
--- a/configs/deneb_defconfig
+++ b/configs/deneb_defconfig
@@ -28,6 +28,8 @@
 CONFIG_AUTOBOOT_PROMPT="Autobooting in %d seconds, press \"<Esc><Esc>\" to stop\n"
 CONFIG_AUTOBOOT_STOP_STR="\x1b\x1b"
 CONFIG_AUTOBOOT_KEYED_CTRLC=y
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="if usrbutton; then run flash_self_test; reset; fi;run flash_self;reset;"
 CONFIG_LOG=y
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SPL_BOARD_INIT=y