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/guruplug_defconfig b/configs/guruplug_defconfig
index 4a9cd23..2e6b8e0 100644
--- a/configs/guruplug_defconfig
+++ b/configs/guruplug_defconfig
@@ -13,6 +13,8 @@
 # CONFIG_SYS_MALLOC_F is not set
 CONFIG_SYS_LOAD_ADDR=0x800000
 CONFIG_BOOTDELAY=3
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="setenv bootargs ${console} ${mtdparts} ${bootargs_root}; ubi part root; ubifsmount ubi:rootfs; ubifsload 0x800000 ${kernel}; ubifsload 0x700000 ${fdt}; ubifsumount; fdt addr 0x700000; fdt resize; fdt chosen; bootz 0x800000 - 0x700000"
 CONFIG_USE_PREBOOT=y
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_HUSH_PARSER=y