drm/amdgpu: change the reference clock for raven/raven2

Due to switch to golden tsc register to get clock counter for raven/ raven2.
Chang the reference clock from 25MHZ to 100MHZ.

Suggested-by: shanshengwang <shansheng.wang@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Jesse Zhang <jesse.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>