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/vf610twr_defconfig b/configs/vf610twr_defconfig
index eafd5b3..2fb69c1 100644
--- a/configs/vf610twr_defconfig
+++ b/configs/vf610twr_defconfig
@@ -15,6 +15,8 @@
 CONFIG_DEFAULT_DEVICE_TREE="vf610-twr"
 CONFIG_SYS_LOAD_ADDR=0x82000000
 CONFIG_BOOTDELAY=3
+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; else run netboot; fi; fi; else run netboot; fi"
 CONFIG_LOGLEVEL=3
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_HUSH_PARSER=y