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/pm9g45_defconfig b/configs/pm9g45_defconfig
index 96260e0..2d63a8c 100644
--- a/configs/pm9g45_defconfig
+++ b/configs/pm9g45_defconfig
@@ -17,6 +17,8 @@
 CONFIG_BOOTDELAY=3
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="fbcon=rotate:3 console=tty0 console=ttyS0,115200 root=/dev/mtdblock4 mtdparts=atmel_nand:128k(bootstrap)ro,256k(uboot)ro,1664k(env),2M(linux)ro,-(root) rw rootfstype=jffs2"
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="nand read 0x70000000 0x200000 0x300000;bootm 0x70000000"
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_HUSH_PARSER=y