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/rzg2_beacon_defconfig b/configs/rzg2_beacon_defconfig
index b9bbc20..9b5f5bc 100644
--- a/configs/rzg2_beacon_defconfig
+++ b/configs/rzg2_beacon_defconfig
@@ -14,6 +14,8 @@
 CONFIG_FIT=y
 CONFIG_SUPPORT_RAW_INITRD=y
 # CONFIG_ARCH_FIXUP_FDT_MEMORY is not set
+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 booti ${loadaddr} - ${fdt_addr}; fi"
 CONFIG_DEFAULT_FDT_FILE="r8a774a1-beacon-rzg2m-kit.dtb"
 # CONFIG_BOARD_EARLY_INIT_F is not set
 CONFIG_HUSH_PARSER=y