.gitignore: Ignore .img files

The generated idbloader.img file that rockchip uses should
be not included in git status report

Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>

.gitignore

@@ -17,6 +17,7 @@
 *.gcda
 *.gcno
 *.i
+*.img
 *.lex.c
 *.lst
 *.mod.c