drm/xe: Move 'vram_flags' flag back to platform descriptor

drm/xe: Move 'vram_flags' flag back to platform descriptor

Restrictions and requirements on VRAM alignment are something that
should be tracked at the platform level rather than the IP level.  Even
when mixing and matching various graphics, media, and display IP blocks,
the platform as a whole has to have consistent memory allocation
handling.  This is also a trait that should be tied to the platform even
if the graphics IP itself is not present (e.g., if we disable the
primary GT via configfs).

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20251013200944.2499947-30-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>