drm/i915/adlp/tc: Use the DE HPD ISR register for hotplug detection

The spec says to use the CPU ISR registers for DP-alt/TBT HPD detection
on ADLP, so do that instead of using the related IOM/TCSS registers.

Bspec: 55480, 55482, 49212, 49305

Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230323142035.1432621-23-imre.deak@intel.com