drm/amd/display: Fix potential memory leak in DMUB hw_init

[Why]
On resume we perform DMUB hw_init which allocates memory:
dm_resume->dm_dmub_hw_init->dc_dmub_srv_create->kzalloc
That results in memory leak in suspend/resume scenarios.

[How]
Allocate memory for the DC wrapper to DMUB only if it was not
allocated before.
No need to reallocate it on suspend/resume.

Signed-off-by: Lang Yu <Lang.Yu@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>