drm/radeon: fix display tiling setup on SI

Apply the same logic as CI to SI for setting up the
display tiling parameters.  The num banks may vary
per tiling index just like CI.

Bugs:
https://bugs.freedesktop.org/show_bug.cgi?id=71488
https://bugs.freedesktop.org/show_bug.cgi?id=73946
https://bugs.freedesktop.org/show_bug.cgi?id=74927



Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org