efi_selftest: Update .gitignore

Add the following file to .gitignore
 efi_miniapp_file_image_exception.h
Signed-off-by: NSughosh Ganu <sughosh.ganu@linaro.org>
Use efi_miniapp_*.h instead of file enumeration.
Signed-off-by: NHeinrich Schuchardt <xypron.glpk@gmx.de>

lib/efi_selftest/.gitignore

-efi_miniapp_file_image_exit.h
-efi_miniapp_file_image_return.h
+efi_miniapp_*.h
 *.efi
 *.so