tcg: Add TCG_OPF_NOT_PRESENT to opcodes without inputs or outputs

tcg: Add TCG_OPF_NOT_PRESENT to opcodes without inputs or outputs

The br, mb, goto_tb and exit_tb opcodes do not have
register operands, only constants, flags, or labels.
Remove the special case in opcode_args_ct by including
TCG_OPF_NOT_PRESENT in the flags for these opcodes.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>