chore: add dependency files generated by tools to .gitignore

In order to avoid git tracking dependency files generated while
compiling tools, the .gitignore list was updated with these files.

Change-Id: I97f1ace40441353779f4f82051d66c478571df38
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>

.gitignore

@@ -11,6 +11,7 @@ build/
 
 # Ignore build products from tools
 tools/**/*.o
+tools/**/*.d
 tools/renesas/rcar_layout_create/*.bin
 tools/renesas/rcar_layout_create/*.srec
 tools/renesas/rcar_layout_create/*.map