Add a basic GPU node for mt8183, as well as OPP table.

Note that with the current panfrost driver, devfreq is not
actually functional, as the we do not have platform-specific
support for >1 supplies. Also, we are missing code to handle
frequency change, as the GPU frequency needs to be switched
away to a stable 26Mhz clock during the transition.
Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Link: https://lore.kernel.org/r/20210521200038.v14.1.I9f45f5c1f975422d58b5904d11546349e9ccdc94@changeidSigned-off-by: Matthias Brugger <matthias.bgg@gmail.com>