drm/xe/pm: Temporarily disable D3Cold on BMG

Currently, many instability cases related to D3Cold -> D0 transition
on BMG are under investigation. Among them some bad cases where
the device is lost after 1 to 3 transitions from D3Cold to D0
on the runtime pm, with pcieport upstream bridge port link retrain
failure.

In other cases, it works fine, but with some sudden random memory
corruptions after D3cold, that could be 0xffff missed ack on GT
forcewake or GuC reload related failures.

In some other cases though, D3Cold -> D0 works pretty reliably.
It looks like it is a combination of GPU cards and Host boards at
this point. So, there is no possible/available quirk at this time.

This patch disables the D3Cold by default on BMG by reducing the
vram_d3cold_threshold to 0. Users and developers who wants to enable
it are still able to via
$ echo 300 > /sys/bus/pci/devices/<addr>/vram_d3cold_threshold

Fixes: 3adcf970 ("drm/xe/bmg: Drop force_probe requirement")
Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/4037
Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/4395
Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/4396


Cc: Karthik Poosa <karthik.poosa@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250308005636.1475420-1-rodrigo.vivi@intel.com


Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>