Makefile: Rename ALL-y to INPUTS-y

When binman is in use, most of the targets built by the Makefile are
inputs to binman. We then need a final rule to run binman to produce the
final outputs.

Rename the variable to indicate this, and add a new 'inputs' target.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/tools/binman/README b/tools/binman/README
index a6a3ee4..37ee3fc 100644
--- a/tools/binman/README
+++ b/tools/binman/README
@@ -220,7 +220,7 @@
 endif
 
 This assumes that u-boot-<your_suffix>.bin is a target, and is the final file
-that you need to produce. You can make it a target by adding it to ALL-y
+that you need to produce. You can make it a target by adding it to INPUTS-y
 either in the main Makefile or in a config.mk file in your arch subdirectory.
 
 Once binman is executed it will pick up its instructions from a device-tree