blackfin: Ignore generated uImages

We have the build infrastructure to generate uImages so we should ignore
the resulting generated files.

Signed-off-by: Mark Brown <broonie@linaro.org>
Acked-by: Mike Frysinger <vapier@gentoo.org>

arch/blackfin/boot/.gitignore

@@ -1,2 +1,3 @@
 vmImage*
 vmlinux*
+uImage*