drm/amd/display: dcn42 don't round up disclk and dppclk

drm/amd/display: dcn42 don't round up disclk and dppclk

[why]
dml2 based on num_enabled clock != 2 to do clock ramming to dpm.
apu has 8 levels dispclk/dppclk/dcfclk/fclk, but only 4 levels of memclk.
to avoid mapping dispclk/dppclk to DPM clock,
based on arch review, force dispclk/dppclk num_level as 2.

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: Charlene Liu <Charlene.Liu@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Signed-off-by: Chuanyu Tseng <Chuanyu.Tseng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>