Allow command-line files to be dropped

These files do not need to be compiled when CONFIG_CMDLINE is disabled.
Update the Makefile to reflect this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>

common/Makefile

@@ -150,10 +150,10 @@ endif
 endif
 
 # We always have this since drivers/ddr/fs/interactive.c needs it
-obj-y += cli_simple.o
+obj-$(CONFIG_CMDLINE) += cli_simple.o
 
 obj-y += cli.o
-obj-y += cli_readline.o
+obj-$(CONFIG_CMDLINE) += cli_readline.o
 obj-y += command.o
 obj-y += s_record.o
 obj-y += xyzModem.o