cmd: Add osd commands

Add command to query information from and write text to on-screen
display (OSD) devices.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/Makefile b/cmd/Makefile
index d3815ab..8f91570 100644
--- a/cmd/Makefile
+++ b/cmd/Makefile
@@ -97,6 +97,7 @@
 obj-$(CONFIG_CMD_NAND) += nand.o
 obj-$(CONFIG_CMD_NET) += net.o
 obj-$(CONFIG_CMD_ONENAND) += onenand.o
+obj-$(CONFIG_CMD_OSD) += osd.o
 obj-$(CONFIG_CMD_PART) += part.o
 ifdef CONFIG_PCI
 obj-$(CONFIG_CMD_PCI) += pci.o