drm/amd/display: Perform DMUB hw_init on resume

[Why]
The DMUB is put into reset on suspend and is not running on resume,
disabling PSR/ABM features.

[How]
Move the allocation of the framebuffer to sw_init.

Do DMUB hardware init and framebuffer filling only from hw_init.

On resume the contents of the framebuffer will be invalid so those
should be cleared.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Roman Li <Roman.Li@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>