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/sama5d27_giantboard_defconfig b/configs/sama5d27_giantboard_defconfig
index 9e0eb67..9ca984c1 100644
--- a/configs/sama5d27_giantboard_defconfig
+++ b/configs/sama5d27_giantboard_defconfig
@@ -34,6 +34,8 @@
 CONFIG_AUTOBOOT_STOP_STR=" "
 CONFIG_AUTOBOOT_KEYED_CTRLC=y
 CONFIG_USE_BOOTARGS=y
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="fatload mmc 0 0x22000000 at91-sama5d27_giantboard.dtb; fatload mmc 0 0x23000000 zImage; bootz 0x23000000 - 0x22000000"
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_MISC_INIT_R=y
 CONFIG_HUSH_PARSER=y