tools/x86/kcpuid: Add .gitignore

Ignore kcpuid ELF file.

  [ bp: Drop the '/' before the name. ]

Signed-off-by: Rong Tao <rtoax@foxmail.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/tencent_F0318BF0724705EC156C341E11DE4040E805@qq.com