drm/amd/display: Force disable planes on any pipe split change

drm/amd/display: Force disable planes on any pipe split change

[Why]
In scenario when 1 display connected with pipe split (2 pipes in use)
and 3 new displays simultaneously hotplugged via MST hub (4 pipes in use),
mpcc may get reprogram to other vtg, remaining busy.
In this case waiting for mpcc idle timeouts with error like this:
[drm] REG_WAIT timeout 1us * 100000 tries - mpc2_assert_idle_mpcc
RIP: 0010:mpc2_assert_mpcc_idle_before_connect
Call Trace:
dcn20_update_mpcc
dcn20_program_front_end_for_ctx
dc_commit_state
amdgpu_dm_atomic_commit_tail
...

[How]
Add pipe split change condition to disable dangling plane.

Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Roman Li <Roman.Li@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>