Add Support for Distance Button Control on Toyota TSS1 with SDSU

[krkeegan]

• Updates the opendbc submodule to the current version with additional commits containing support for the SDSU FD_BUTTON message.

• Updates the Cereal Submodule to a version with hasSmartDSU support.

Note this will require that the SDSU has at least this firmware on it, in order for the distance button signal to be forwarded: https://github.com/wocsor/panda/commit/b5120f6427551345c543b490fe47da189c1e48e1

I also updated the documentation, including notes for hide_model_long and df_button_alerts that were in a previously merged PR.

[sshane]

Merged the cereal PR; can you update the cereal submodule so it's at sshane/cereal:master (9b56d02dd8fe800c651d5ccace7b0acd69584a7c)?

[krkeegan]

Done.