objtool: Properly disable uaccess validation

If opts.uaccess isn't set, the uaccess validation is disabled, but only
partially: it doesn't read the uaccess_safe_builtin list but still tries
to do the validation.  Disable it completely to prevent false warnings.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/0e95581c1d2107fb5f59418edf2b26bba38b0cbb.1742852846.git.jpoimboe@kernel.org