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/Makefile b/boot/Makefile
index 3fd048b..de0eafe 100644
--- a/boot/Makefile
+++ b/boot/Makefile
@@ -25,6 +25,8 @@
 obj-$(CONFIG_$(SPL_TPL_)BOOTSTD) += bootmeth-uclass.o
 obj-$(CONFIG_$(SPL_TPL_)BOOTSTD) += bootstd-uclass.o
 
+obj-$(CONFIG_$(SPL_TPL_)BOOTSTD_PROG) += prog_boot.o
+
 obj-$(CONFIG_$(SPL_TPL_)BOOTMETH_EXTLINUX) += bootmeth_extlinux.o
 obj-$(CONFIG_$(SPL_TPL_)BOOTMETH_EXTLINUX_PXE) += bootmeth_pxe.o
 obj-$(CONFIG_$(SPL_TPL_)BOOTMETH_EFILOADER) += bootmeth_efi.o