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/nas220_defconfig b/configs/nas220_defconfig
index 386ebca..581d845 100644
--- a/configs/nas220_defconfig
+++ b/configs/nas220_defconfig
@@ -13,6 +13,7 @@
 # CONFIG_SYS_MALLOC_F is not set
 CONFIG_SYS_LOAD_ADDR=0x800000
 CONFIG_BOOTDELAY=3
+CONFIG_USE_BOOTCOMMAND=y
 CONFIG_USE_PREBOOT=y
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_HUSH_PARSER=y