drm/amd/display: Move 'struct scaler_data' off stack

The scaler_data structure is implicitly copied onto the stack twice by
being returned from a function. This is usually a bad idea, but it
was not flagged by the compiler until a recent addition that pushed
it over the 1024 byte function stack limit:

drivers/gpu/drm/amd/amdgpu/../display/dc/dml2/dml2_translation_helper.c: In function 'populate_dml_plane_cfg_from_plane_state':
drivers/gpu/drm/amd/amdgpu/../display/dc/dml2/dml2_translation_helper.c:1075:1: error: the frame size of 1032 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]

Use an explicit kzalloc() and memcpy() instead here to keep it off the
stack.

Fixes: 00c39110 ("drm/amd/display: Add misc DC changes for DCN401")
Fixes: 7966f319 ("drm/amd/display: Introduce DML2")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>