drm/amd/display: flicking observed while installing driver on Navi10 CF

[WHY] value of dchub_ref_clock is decided by dchubbub global timer
settings which is programmed by vbios command table disp_init.
for multi-GPU case, vbios is posted only for primary GPU. without
vbios posted for the secondary GPU, value of dchub_ref_clock is not
set properly. this value will affect dcn bandwidth calcuation and
cause underflow. user will see screen flicking during driver
installation for dual GPU case.

[HOW] dc init_hw always call vbios command table disp_init to
make sure dchubbub global timer is configured and enable.

Signed-off-by: hersen wu <hersenxs.wu@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>