drm/amd/display: disable dcn10 pipe split by default

drm/amd/display: disable dcn10 pipe split by default

[Why]
The initial purpose of dcn10 pipe split is to support some high
bandwidth mode which requires dispclk greater than max dispclk. By
initial bring up power measurement data, it showed power consumption is
less with pipe split for dcn block. This could be reason for enable pipe
split by default. By battery life measurement of some Chromebooks,
result shows battery life is longer with pipe split disabled.

[How]
Disable pipe split by default. Pipe split could be still enabled when
required dispclk is greater than max dispclk.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Hersen Wu <hersenxs.wu@amd.com>
Signed-off-by: Roman Li <Roman.Li@amd.com>
Reviewed-by: Roman Li <Roman.Li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>