drm/amd/display: Change Navi14's DWB flag to 1

[Why]
DWB (Display Writeback) flag needs to be enabled as 1, or system
will throw out a few warnings when creating dcn20 resource pool.
Also, Navi14's dwb setting needs to match Navi10's,
which has already been set to 1.

[How]
Change value of num_dwb from 0 to 1.

Signed-off-by: Zhan Liu <zhan.liu@amd.com>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>