spl: add overall SPL size check

This adds a size check for SPL that can dynamically check generated
SPL binaries (including devicetree) for a size limit that ensures
this image plus global data, heap and stack fit in initial SRAM.

Since some of these sizes are not available to make, a new host tool
'spl_size_limit' is added that dumps the resulting maximum size for
an SPL binary to stdout. This tool is used in toplevel Makefile to
implement the size check on SPL binaries.

Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
diff --git a/tools/Makefile b/tools/Makefile
index e2f572c..33e90a8 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -199,6 +199,10 @@
 hostprogs-y += fdtgrep
 fdtgrep-objs += $(LIBFDT_OBJS) fdtgrep.o
 
+ifneq ($(TOOLS_ONLY),y)
+hostprogs-y += spl_size_limit
+endif
+
 hostprogs-$(CONFIG_MIPS) += mips-relocs
 
 # We build some files with extra pedantic flags to try to minimize things