drm/amd/display: update DCN2 uclk switch time

[why]
value commited to by HW team is going to be higher
than pre-silicon, and will cause underflow if driver not
updated

[how]
update hardcoded value, update pstate switching logic
to fix case where with long uclk time we won't allow switch
even when we should

Signed-off-by: Jun Lei <Jun.Lei@amd.com>
Reviewed-by: Eric Yang <eric.yang2@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>