drm/amd/display: expose additional modifier for DCN32/321

[Why&How]
Some userspace expect a backwards compatible modifier on DCN32/321. For
hardware with num_pipes more than 16, we expose the most efficient
modifier first. As a fall back method, we need to expose slightly inefficient
modifier AMD_FMT_MOD_TILE_GFX9_64K_R_X after the best option.

Also set the number of packers to fixed value as required per hardware
documentation. This value is cached during hardware initialization and
can be read through the base driver.

Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>