ELF uapi: add spaces before '{'

When searching for a struct definition I often enough end up simply doing

  git grep 'struct foobar {'

Sadly some of the ELF structs did not follow the usual coding style so they
were invisible.

Signed-off-by: Rolf Eike Beer <eb@emlix.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/11563980.Ss37MnutNL@mobilepool36.emlix.com