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/liteboard_defconfig b/configs/liteboard_defconfig
index ab62c20..041495f 100644
--- a/configs/liteboard_defconfig
+++ b/configs/liteboard_defconfig
@@ -20,6 +20,8 @@
 CONFIG_SPL=y
 CONFIG_SUPPORT_RAW_INITRD=y
 CONFIG_BOOTDELAY=1
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="mmc dev ${mmcdev};if mmc rescan; then if run loadbootscript; then run bootscript; else if run loadimage; then run mmcboot; else run netboot; fi; fi; else run netboot; fi"
 CONFIG_DEFAULT_FDT_FILE="imx6ul-liteboard.dtb"
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SPL_WATCHDOG=y