drm/amd/display: Update FCLK change latency

drm/amd/display: Update FCLK change latency

[Descrtipion]
- Driver hardcoded FCLK P-State latency was incorrect
- Use the value provided by PMFW header instead

Reviewed-by: Nevenko Stupar <Nevenko.Stupar@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alvin Lee <Alvin.Lee2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>