add cscope.* to .gitignore

we have "make cscope", therefore that makes sense to have cscope.* in
.gitignore.

Signed-off-by: Jun Koi <junkoi2004@gmail.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

.gitignore

@@ -53,3 +53,4 @@ pc-bios/optionrom/linuxboot.bin
 pc-bios/optionrom/multiboot.bin
 pc-bios/optionrom/multiboot.raw
 .stgit-*
+cscope.*