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/warp7_defconfig b/configs/warp7_defconfig
index 3e2ea6a..a76565e 100644
--- a/configs/warp7_defconfig
+++ b/configs/warp7_defconfig
@@ -17,6 +17,8 @@
 CONFIG_IMX_HAB=y
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="mmc dev ${mmcdev};mmc dev ${mmcdev}; if mmc rescan; then run do_bootscript_hab;if run loadbootscript; then run bootscript; else if run loadimage; then run mmcboot; fi; fi; fi"
 CONFIG_HUSH_PARSER=y
 # CONFIG_CMD_BOOTD is not set
 CONFIG_CMD_BOOTZ=y