drm/amd/powrplay: add interface for dc to get max clock values

dc (display component) needs maximum clock values of uclock,
socclk, dcefclk, to calculate display bandwidth.

Signed-off-by: hersen wu <hersenxs.wu@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>