microblaze: Add .gitignore entries for auto-generated files

Add .gitignore entries for files which are generated during the build process.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>

arch/microblaze/boot/.gitignore

@@ -0,0 +1,3 @@
+*.dtb
+linux.bin*
+simpleImage.*

arch/microblaze/kernel/.gitignore

@@ -0,0 +1 @@
+vmlinux.lds