drm/radeon: set default clocks for SI when DPM is disabled

Fix patching of vddc values for SI and enable manually forcing
clocks to default levels as per NI.

This improves the out of the box performance with SI asics.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --cc drivers/gpu/drm/radeon/evergreen.c
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_atombios.c
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_pm.c
Simple merge