drm/amd/display: fix missing .is_two_pixels_per_container

Starting from 6.11, AMDGPU driver, while being loaded with amdgpu.dc=1,
due to lack of .is_two_pixels_per_container function in dce60_tg_funcs,
causes a NULL pointer dereference on PCs with old GPUs, such as R9 280X.

So this fix adds missing .is_two_pixels_per_container to dce60_tg_funcs.

Reported-by: Rosen Penev <rosenp@gmail.com>
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3942


Fixes: e6a901a0 ("drm/amd/display: use even ODM slice width for two pixels per container")
Signed-off-by: Aliaksei Urbanski <aliaksei.urbanski@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>