drm/xe/display: handle HPD polling in display runtime suspend/resume

drm/xe/display: handle HPD polling in display runtime suspend/resume

In XE, display runtime suspend / resume routines are called only
if d3cold is allowed. This makes the driver unable to detect any
HPDs once the device goes into runtime suspend state in platforms
like LNL. Update the display runtime suspend / resume routines
to include HPD polling regardless of d3cold status.

While xe_display_pm_suspend/resume() performs steps during runtime
suspend/resume that shouldn't happen, like suspending MST and they
are missing other steps like enabling DC9, this patchset is meant
to keep the current behavior wrt. these, leaving the corresponding
updates for a follow-up

v2: have a separate function for display runtime s/r (Rodrigo)

v3: better streamlining of system s/r and runtime s/r calls (Imre)

v4: rebased

Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Signed-off-by: Vinod Govindapillai <vinod.govindapillai@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240823112148.327015-4-vinod.govindapillai@intel.com