drm/xe: improve hibernation on igpu

drm/xe: improve hibernation on igpu

The GGTT looks to be stored inside stolen memory on igpu which is not
treated as normal RAM.  The core kernel skips this memory range when
creating the hibernation image, therefore when coming back from
hibernation the GGTT programming is lost. This seems to cause issues
with broken resume where GuC FW fails to load:

[drm] *ERROR* GT0: load failed: status = 0x400000A0, time = 10ms, freq = 1250MHz (req 1300MHz), done = -1
[drm] *ERROR* GT0: load failed: status: Reset = 0, BootROM = 0x50, UKernel = 0x00, MIA = 0x00, Auth = 0x01
[drm] *ERROR* GT0: firmware signature verification failed
[drm] *ERROR* CRITICAL: Xe has declared device 0000:00:02.0 as wedged.

Current GGTT users are kernel internal and tracked as pinned, so it
should be possible to hook into the existing save/restore logic that we
use for dgpu, where the actual evict is skipped but on restore we
importantly restore the GGTT programming.  This has been confirmed to
fix hibernation on at least ADL and MTL, though likely all igpu
platforms are affected.

This also means we have a hole in our testing, where the existing s4
tests only really test the driver hooks, and don't go as far as actually
rebooting and restoring from the hibernation image and in turn powering
down RAM (and therefore losing the contents of stolen).

v2 (Brost)
 - Remove extra newline and drop unnecessary parentheses.

Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/3275
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: <stable@vger.kernel.org> # v6.8+
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241101170156.213490-2-matthew.auld@intel.com