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/devkit3250_defconfig b/configs/devkit3250_defconfig
index 47f730c..98e588f 100644
--- a/configs/devkit3250_defconfig
+++ b/configs/devkit3250_defconfig
@@ -18,6 +18,8 @@
 CONFIG_BOOTDELAY=1
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="console=ttyS0,115200n8"
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="dhcp; tftp ${loadaddr} ${serverip}:${tftpdir}/${bootfile}; tftp ${dtbaddr} ${serverip}:${tftpdir}/devkit3250.dtb; setenv nfsargs ip=dhcp root=/dev/nfs nfsroot=${serverip}:${nfsroot},tcp; setenv bootargs ${bootargs} ${nfsargs} ${userargs}; bootm ${loadaddr} - ${dtbaddr}"
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SPL_BOARD_INIT=y