drm/xe/vram: drop 2G block restriction

Currently we limit the max block size for all users to ensure each block
can fit within a sg entry (uint). Drop this restriction and tweak the sg
construction to instead handle this itself and break down blocks which
are too big, if needed. Most users don't need an sg list in the first
place.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Satyanarayana K V P <satyanarayana.k.v.p@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Tested-by: Satyanarayana K V P <satyanarayana.k.v.p@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241113172346.256165-2-matthew.auld@intel.com