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/stv0991_defconfig b/configs/stv0991_defconfig
index f46efa6..fa1ae10 100644
--- a/configs/stv0991_defconfig
+++ b/configs/stv0991_defconfig
@@ -16,6 +16,8 @@
 CONFIG_AUTOBOOT_KEYED=y
 CONFIG_AUTOBOOT_PROMPT="Hit SPACE in %d seconds to stop autoboot.\n"
 CONFIG_AUTOBOOT_STOP_STR=" "
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="go 0x40040000"
 # CONFIG_DISPLAY_CPUINFO is not set
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_BOARD_EARLY_INIT_F=y