drm/amd/display: Default IPS to RCG_IN_ACTIVE_IPS2_IN_OFF

[Why]

Recent findings show negligible power savings between IPS2 and RCG
during static desktop. In fact, DCN related clocks are higher
when IPS2 is enabled vs RCG.

RCG_IN_ACTIVE is also the default policy for another OS supported by
DC, and it has faster entry/exit.

[How]

Remove previous logic that checked for IPS2 support, and just default
to `DMUB_IPS_RCG_IN_ACTIVE_IPS2_IN_OFF`.

Fixes: 199888aa ("drm/amd/display: Update IPS default mode for DCN35/DCN351")
Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Tested-by: Mark Broadworth <mark.broadworth@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 8f772d79)
Cc: stable@vger.kernel.org