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/tplink_wdr4300_defconfig b/configs/tplink_wdr4300_defconfig
index 6b55c93..5de4ada 100644
--- a/configs/tplink_wdr4300_defconfig
+++ b/configs/tplink_wdr4300_defconfig
@@ -12,6 +12,8 @@
 CONFIG_BOOTDELAY=3
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="console=ttyS0,115200 root=/dev/mtdblock2 rootfstype=squashfs"
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="dhcp 192.168.1.1:wdr4300.fit && bootm $loadaddr"
 CONFIG_DISPLAY_CPUINFO=y
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_HUSH_PARSER=y