drm/amd/display: Allow dmub srv hardware reset before HW init

[Why]
We need hardware reset before hardware init for backdoor loading when
we're reusing the framebuffer memory.

[How]
This doesn't run if the hardware isn't already in reset from software
perspective. The reset function has register level checks so just
remove the software one here.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Eric Yang <eric.yang2@amd.com>
Acked-by: Anson Jacob <anson.jacob@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>