ac/surface: Handle non-retiled displayable DCC correctly for modifiers.

ac/surface: Handle non-retiled displayable DCC correctly for modifiers.

There is some hardware with num_render_backends == 1, but the number
of render backends in GB_ADDR_CFG > 1. Turns out this can be turned
off by making them rb unaligned which is valid with only 1 render
backend.

Fixes: 0833dd7d124 ("amd/common: Add support for modifiers.")
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10575>