drm/amd/display: Detect plane change when detect pipe change.

[Why]
If plane has changed, dcn20_detect_pipe_changes doesn't update dc_plane_state->update_flags, and the following dcn20_program_pipe can't reprogram hubp correctly.

[How]
Add a new flags bit "plane_changed" in pipe_ctx->update_flags.If old plane isn’t identical to new plane, this bit will be set and guide “dcn20_program_pipe” to programing HUBP correctly.

Signed-off-by: JinZe.Xu <JinZe.Xu@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>