drm/amd/display: fix dcn3 p_state_change_support validation (v2)

drm/amd/display: fix dcn3 p_state_change_support validation (v2)

Our validation is a known mess with actual validation mixed with
topology configuration. This change makes sure topolgical validation is
completed before any topology changes are made so we do not run into
issues where we merge and split a pipe over the course of a single call.

v2: Squash in compilation fix

Signed-off-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>