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/efi-x86_payload64_defconfig b/configs/efi-x86_payload64_defconfig
index 26cfc49..36dd064 100644
--- a/configs/efi-x86_payload64_defconfig
+++ b/configs/efi-x86_payload64_defconfig
@@ -10,6 +10,8 @@
 CONFIG_SHOW_BOOT_PROGRESS=y
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="root=/dev/sdb3 init=/sbin/init rootwait ro"
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="ext2load scsi 0:3 01000000 /boot/vmlinuz; zboot 01000000"
 CONFIG_PRE_CONSOLE_BUFFER=y
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
 CONFIG_DISPLAY_BOARDINFO_LATE=y