gitignore: Add MIPS vmlinux.32 to the list

MIPS64 kernels builds will produce a vmlinux.32 kernel image for
compatibility, ignore them.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>

.gitignore

@@ -44,6 +44,7 @@ Module.symvers
 /TAGS
 /linux
 /vmlinux
+/vmlinux.32
 /vmlinux-gdb.py
 /vmlinuz
 /System.map