drm/amd/display: Poll analog connectors (v3)

drm/amd/display: Poll analog connectors (v3)

VGA connectors don't support any hotplug detection, so the kernel
needs to periodically poll them to see if a display is connected.

DVI-I connectors have hotplug detection for digital signals, and
some analog DVI cables pull up that pin to work with that.
However, in general not all DVI cables do this so we can't rely on
this feature, therefore we need to poll DVI-I connectors as well.

v2:
Call drm_kms_helper_poll_fini in amdgpu_dm_hpd_fini.
Disable/enable polling on suspend/resume.
Don't call full link detection when already connected.

v3:
Encounter CLANG build failure. Remove unused variable:
drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm_irq.c:980:7:
error: variable 'use_polling' set but not used [-Werror,-Wunused-but-
set-variable]
980 |         bool use_polling = false;

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>