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/at91sam9g20ek_dataflash_cs0_defconfig b/configs/at91sam9g20ek_dataflash_cs0_defconfig
index 12d7fd3..9fb18c2 100644
--- a/configs/at91sam9g20ek_dataflash_cs0_defconfig
+++ b/configs/at91sam9g20ek_dataflash_cs0_defconfig
@@ -21,6 +21,8 @@
 CONFIG_BOOTDELAY=3
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="console=ttyS0,115200 root=/dev/mtdblock0 mtdparts=atmel_nand:-(root) rw rootfstype=jffs2"
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="sf probe 0:0; sf read 0x22000000 0x84000 0x294000; bootm 0x22000000"
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_SYS_PROMPT="U-Boot> "
 # CONFIG_CMD_BDI is not set