drm/amd/pm: update the LC_L1_INACTIVITY setting to address possible noise issue

It is proved that insufficient LC_L1_INACTIVITY setting can cause audio
noise on some platform. With the LC_L1_INACTIVITY increased to 4ms, the
issue can be resolved.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>