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/somlabs_visionsom_6ull_defconfig b/configs/somlabs_visionsom_6ull_defconfig
index 7dad016..956a6ca 100644
--- a/configs/somlabs_visionsom_6ull_defconfig
+++ b/configs/somlabs_visionsom_6ull_defconfig
@@ -12,6 +12,8 @@
 CONFIG_DEFAULT_DEVICE_TREE="imx6ull-somlabs-visionsom"
 CONFIG_FIT=y
 CONFIG_SUPPORT_RAW_INITRD=y
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="run setfdtfile; run checkbootdev; run loadfdt;if run loadbootscript; then run bootscript; else if run loadimage; then run setbootargs; bootz ${loadaddr} - ${fdt_addr}; fi; fi"
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y