drm/xe: Implement and use the drm_pagemap populate_mm op

drm/xe: Implement and use the drm_pagemap populate_mm op

Add runtime PM since we might call populate_mm on a foreign device.

v3:
- Fix a kerneldoc failure (Matt Brost)
- Revert the bo type change from device to kernel (Matt Brost)
v4:
- Add an assert in xe_svm_alloc_vram (Matt Brost)

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20250619134035.170086-4-thomas.hellstrom@linux.intel.com