bootstd: Introduce programmatic boot

At present bootstd requires CONFIG_CMDLINE to operate. Add a new
'programmatic' boot which can be used when no command line is available.
For now it does almost nothing, since most bootmeths require the
command line.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/boot/Kconfig b/boot/Kconfig
index ef71883..b438002 100644
--- a/boot/Kconfig
+++ b/boot/Kconfig
@@ -459,6 +459,18 @@
 	  standard boot does not support all of the features of distro boot
 	  yet.
 
+config BOOTSTD_PROG
+	bool "Use programmatic boot"
+	depends on !CMDLINE
+	default y
+	help
+	  Enable this to provide a board_run_command() function which can boot
+	  a systen without using commands. If the boot fails, then U-Boot will
+	  panic.
+
+	  Note: This currently has many limitations and is not a useful booting
+	  solution. Future work will eventually make this a viable option.
+
 config BOOTMETH_GLOBAL
 	bool
 	help