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/ds414_defconfig b/configs/ds414_defconfig
index 4b867bc..773dbc1 100644
--- a/configs/ds414_defconfig
+++ b/configs/ds414_defconfig
@@ -27,6 +27,8 @@
 CONFIG_BOOTDELAY=3
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="console=ttyS0,115200 ip=off initrd=0x8000040,8M root=/dev/md0 rw syno_hw_version=DS414r1 ihd_num=4 netif_num=2 flash_size=8 SataLedSpecial=1 HddHotplug=1"
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="sf probe; sf read ${loadaddr} 0xd0000 0x2d0000; sf read ${ramdisk_addr_r} 0x3a0000 0x430000; bootm ${loadaddr} ${ramdisk_addr_r}"
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_DISPLAY_BOARDINFO_LATE=y
 CONFIG_MISC_INIT_R=y