drm/amd/display: Update IPS default mode for DCN35/DCN351

[WHY]
RCG state of IPX in idle is more stable for DCN351 and some variants of
DCN35 than IPS2.

[HOW]
Rework dm_get_default_ips_mode() to specify default per ASIC and update
DCN35/DCN351 defaults accordingly.

Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Reviewed-by: Sun peng Li <sunpeng.li@amd.com>
Signed-off-by: Roman Li <Roman.Li@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>