turnip: Add a618 support

turnip: Add a618 support

I merely ported a freedreno patch to turnip which
updates some magic regsiter values.

    commit ff6e148a3d60e6e7f3b33f134228b1ed4216903e
    Author:     Rob Clark <robdclark@chromium.org>
    CommitDate: Tue Oct 29 09:19:34 2019 -0700
    Subject:    freedreno/a6xx: add a618 support

That's all that Rob did for gallium for a618, so I assume that's we need
for turnip also.

Tested manually with:

    dEQP-VK.api.image_clearing.core.clear_color_image.2d.linear.single_layer.*
        pass 300/555
        fail   0/555
        skip 255/555

Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3743>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3743>