drm/amd/display: Fix DPSTREAM CLK on and off sequence

[Why]
Secondary DP2 display fails to light up in some instances

[How]
Clock needs to be on when DPSTREAMCLK*_EN =1. This change
moves dtbclk_p enable/disable point to make sure this is
the case

Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Reviewed-by: Dmytro Laktyushkin <dmytro.laktyushkin@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Daniel Miess <daniel.miess@amd.com>
Signed-off-by: Dmytro Laktyushkin <dmytro.laktyushkin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>