drm/amd/display: "Enable IPS by default"

[Why]
IPS was temporary disabled due to instability.
It was fixed in dmub firmware and with:
- "drm/amd/display: Add IPS checks before dcn register access"
- "drm/amd/display: Disable ips before dc interrupt setting"

[How]
Enable IPS by default.
Disable IPS if 0x800 bit set in amdgpu.dcdebugmask module params

Signed-off-by: Roman Li <Roman.Li@amd.com>
Tested-by: Mark Broadworth <mark.broadworth@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>